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 By: Tping (offline)  Wednesday, June 06 2012 @ 12:28 AM CDT (Read 3965 times)
Tping

1)
Shane only carries \$5 and \$2 note in his waist pouch.
He saw a printer which cost \$298 and bought it with 77 pieces of notes from his pouch.
Find the total value of all the \$5 notes he has in the pouch at first
if the number of \$5 notes he had originally is 14
more than the number of \$5 notes he used to pay for the printer.

2)
One bright and early morning, a snail fell into a well that is 3m deep.
Every day, he would climb 1/5m up the well and by evening he would slide down 1/10m.
How many days would the snail take to get out of the well if he continued at this rate?

Junior

Registered: 01/26/12
Posts: 25

 By: awyw1201 (offline)  Wednesday, June 06 2012 @ 11:32 AM CDT
awyw1201

Quote by: Tping

1)
Shane only carries \$5 and \$2 note in his waist pouch.
He saw a printer which cost \$298 and bought it with 77 pieces of notes from his pouch.
Find the total value of all the \$5 notes he has in the pouch at first
if the number of \$5 notes he had originally is 14
more than the number of \$5 notes he used to pay for the printer.

2)
One bright and early morning, a snail fell into a well that is 3m deep.
Every day, he would climb 1/5m up the well and by evening he would slide down 1/10m.
How many days would the snail take to get out of the well if he continued at this rate?

1) Suppose all 77 notes are \$2 notes.

77 x \$2 = \$154
\$298 - \$154 = \$144
Diff btw one \$5 note and one \$2 note = \$3
\$144/\$3 = 48 (No. of \$5 notes used)
Value of \$5 notes at first--- (48 + 14) x \$5 = \$310

Ans: \$310

2) Day 1--> 0.2m - 0.1m = 0.1m
Day 2-->0.1m +0.2m - 0.1m = 0.2m
Day 3--> 0.2m + 0.2m - 0.1m = 0.3m

From the pattern above, we reckon by Day 28, the snail would have climbed 2.8m.

Day 29 --> 2.8m + 0.2m = 3m ( snail would be out of well!)

Ans: 29 days

Regular Member

Registered: 07/08/11
Posts: 87

 By: Tping (offline)  Wednesday, June 06 2012 @ 09:55 PM CDT
Tping

Thank you ~

Junior

Registered: 01/26/12
Posts: 25

 By: echeewh (offline)  Thursday, June 07 2012 @ 08:57 PM CDT
echeewh

Hey there,

Following pls find another solution for
Q1 ( without using Guess & Check / Assume ALL methods - such methods may be not be awarded the full method marks if there's a proper method in doing it.)

Let the number of \$5 notes at first be 1u.
Hence, number of \$5 notes used = 1u -14
Given that 77 notes were used,
number of \$2 notes used = 77 - (1u - 14) = 91 - 1u

Using Number x Value method, we have ...

[(1u - 14) x 5] + [(91 - 1u) x 2] --> 298
(5u - 70) + (182 - 2u) --> 298
3u --> 298 + 70 - 182 = 186
1u --> 186 ÷ 3 = 62

Total value of all \$5 notes at first = 62 x 5 = \$310

=====================================

Q2.

Believe there's a mistake ( in red ) made in awyw1201's solution.

Day 29 --> 2.8m + 0.2m = 3m

This is incorrect because for each day, the snail could only climb 0.1m ( and not 0.2m) as shown above. Presumably its a typo error
Hence, it should be in Day 30 as provided in my alternative worked solution as follows:

Here's my worked solution:

1day, length / dist covered by snail = 1/5 - 1/10 = 1/10 m
Given that the well is 3m deep, number of days to climb out = 3 ÷ (1/10) = 3 x 10 = 30

======================================

Trust this helps.

Cheers,
Edward

Active Member

Registered: 04/21/11
Posts: 627

 By: awyw1201 (offline)  Thursday, June 07 2012 @ 10:48 PM CDT
awyw1201

Quote by: echeewh

Hey there,

Following pls find another solution for
Q1 ( without using Guess & Check / Assume ALL methods - such methods may be not be awarded the full method marks if there's a proper method in doing it.)

Let the number of \$5 notes at first be 1u.
Hence, number of \$5 notes used = 1u -14
Given that 77 notes were used,
number of \$2 notes used = 77 - (1u - 14) = 91 - 1u

Using Number x Value method, we have ...

[(1u - 14) x 5] + [(91 - 1u) x 2] --> 298
(5u - 70) + (182 - 2u) --> 298
3u --> 298 + 70 - 182 = 186
1u --> 186 ÷ 3 = 62

Total value of all \$5 notes at first = 62 x 5 = \$310

=====================================

Q2.

Believe there's a mistake ( in red ) made in awyw1201's solution.

Day 29 --> 2.8m + 0.2m = 3m

This is incorrect because for each day, the snail could only climb 0.1m ( and not 0.2m) as shown above. Presumably its a typo error
Hence, it should be in Day 30 as provided in my alternative worked solution as follows:

Here's my worked solution:

1day, length / dist covered by snail = 1/5 - 1/10 = 1/10 m
Given that the well is 3m deep, number of days to climb out = 3 ÷ (1/10) = 3 x 10 = 30

======================================

Trust this helps.

Cheers,
Edward

Hi Edward, for qn 1, I've though the assumption method to my son and he used the same method for worksheets and tests. The teacher marked him correct so I do not agree that this method will not be granted full marks. Furthermore, my take is in that in Math, there is no "proper" methods, as long as they r logical, we should accept them.

For qn 2, if u look carefully, there was no typo on my part, the snail climb up 0.2m and slide down 0.1m each day. At the start of day 29, the snail would have climbed 2.8m +0.2m, it's already out of the well, there's no need for it to slide back 0.1m!

Thanks:-)

Regular Member

Registered: 07/08/11
Posts: 87

 By: awyw1201 (offline)  Thursday, June 07 2012 @ 10:55 PM CDT
awyw1201

Sorry, now there's really a typo: should be I've taught my son:-)

Regular Member

Registered: 07/08/11
Posts: 87

 By: echeewh (offline)  Saturday, June 09 2012 @ 04:45 PM CDT
echeewh

Hey awyw1201 ( to whom it may concern ),

I have to agree to disagree ..

First of all, I dont think this is a platform to debate / argue / challenge over sharing of info , as this may confuse the audience reading it ( be it parents or children / students ).

Secondly, I feel its rather unwise of you ( as an adult parent ) to discredit/ criticize someone's kind intention of sharing the experience / knowledge with the audience here ( without any prior findings )

About Guess& Check / Assume ALL methods, these are methods used to solve typical problems in which no other correct / 'proper' methods can be used. Typically these are questions in which insufficient data / info are provided to allow correct / 'proper' method(s) to be used.

In your experience with your son, it could possibly be the Assume ALL method is applied to / used for the 'correct' / typical question itself.

Let me extract out a quote from the Marking Scheme for Raffles Girls' Primary.

Quote
No Marks will be awarded for correct answer with wrong method.
Unquote

Whether or not I get my facts right, yes of course I do. I have seen different marking schemes from about 10 or more schools and encountered situation in which 0 mark is given for Guess& Check / Assume ALL method used in questions where correct / 'proper' method(s) can be used.

Hence, I find its important to share this out with parents and students concerned. Again, whether 0 mark is awarded or not, depends very much on the marker and/or school. My advice is use other correct methods first and take this as a final resort. Exception is to use this method for those typical kind of questions ( where such methods are used ). Again, its always to be 'safe than sorry'. Morale of the story is 'dont take risk' / 'never take chances' like this as it may cause you 0 Method marks, and the opportunity to get a better score that may lead to a better grade.

To All concerned: Pls take this a word of caution and I shall leave this matter in your own hands ( for you to decide ).

Best regards.
Edward

Active Member

Registered: 04/21/11
Posts: 627

 By: awyw1201 (offline)  Thursday, June 14 2012 @ 10:59 PM CDT
awyw1201

Quote by: echeewh

Hey awyw1201 ( to whom it may concern ),

I have to agree to disagree ..

First of all, I dont think this is a platform to debate / argue / challenge over sharing of info , as this may confuse the audience reading it ( be it parents or children / students ).

Secondly, I feel its rather unwise of you ( as an adult parent ) to discredit/ criticize someone's kind intention of sharing the experience / knowledge with the audience here ( without any prior findings )

About Guess& Check / Assume ALL methods, these are methods used to solve typical problems in which no other correct / 'proper' methods can be used. Typically these are questions in which insufficient data / info are provided to allow correct / 'proper' method(s) to be used.

In your experience with your son, it could possibly be the Assume ALL method is applied to / used for the 'correct' / typical question itself.

Let me extract out a quote from the Marking Scheme for Raffles Girls' Primary.

Quote

No Marks will be awarded for correct answer with wrong method.
Unquote

Whether or not I get my facts right, yes of course I do. I have seen different marking schemes from about 10 or more schools and encountered situation in which 0 mark is given for Guess& Check / Assume ALL method used in questions where correct / 'proper' method(s) can be used.

Hence, I find its important to share this out with parents and students concerned. Again, whether 0 mark is awarded or not, depends very much on the marker and/or school. My advice is use other correct methods first and take this as a final resort. Exception is to use this method for those typical kind of questions ( where such methods are used ). Again, its always to be 'safe than sorry'. Morale of the story is 'dont take risk' / 'never take chances' like this as it may cause you 0 Method marks, and the opportunity to get a better score that may lead to a better grade.

To All concerned: Pls take this a word of caution and I shall leave this matter in your own hands ( for you to decide ).

Best regards.
Edward

Hi Edward,

Let me assure u that it was not my intention to "confuse" the viewers. I was merely giving the viewers here another alternative method which, in my opinion, was much efficient especially when students are trying to solve so many challenging problems within the allotted time. Time is the essence, isn't it? If the child is able to understand the assumption method, why resort to "long-winded" methods? But I concur that not all students will be able to understand the assumption method but as parents, we want to push our children a little further, don't we? After all, it's about practice. As for the Guess and Check method, I do not particularly like this method and I would advise all to use that as a last resort.

I did not mean to discredit your good intentions, if I do, I sincerely apologize. I do not know the marking schemes for all schools but I happen to have a close friend who taught Maths In RGPS. She clarified that the sentence u quote "No Marks will be awarded for correct answer with wrong method" is meant for fluke answers, that is answer happens to be correct but the methods are wrong. This also applies to PSLE. She also mentioned Guess and Check method and assumption method are acceptable methods, but not wrong methods.

Thank you:-)

Regular Member

Registered: 07/08/11
Posts: 87

 By: echeewh (offline)  Friday, June 15 2012 @ 12:15 AM CDT
echeewh

FYI: My proposed method is logical and I dont think its 'long-winded' as compared to the Assumption ALL method. Its only a couple more lines or 'number statements' used. In that essence, one is assured of the full method marks and avoid any possibility of not getting it in full.

Active Member

Registered: 04/21/11
Posts: 627

 By: awyw1201 (offline)  Friday, June 15 2012 @ 11:56 AM CDT
awyw1201

Hi Edward,
A couple of more steps in tackling word problems, especially under stressful exam conditions, are breeding grounds for computational errors (even with calculators!). Thus, if there r more efficient and legitimate methods, why not learn them? If someone were to show me a different method that is able to solve this particular question posted in this thread in one step, I would gladly grab the opportunity to learn it! Anyway, it was nice talking to u. Pls bear in mind I was disagreeable to your words posted on 7 June: "Following pls find another solution for
Q1 ( without using Guess & Check / Assume ALL methods - such methods may be not be awarded the full method marks if there's a proper method in doing it.)

I maintained my stand: assumption method will be awarded full method marks.

Thank you:-)

Regular Member

Registered: 07/08/11
Posts: 87

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