
By: pearldyn (offline) Thursday, April 08 2010 @ 07:46 PM CDT (Read 1400 times)



pearldyn 
Hi again!
Any takers on this one?
An MRT train was 2/5 full of passengers. At the first station, 1/2 of the passengers alighted
and 17 people boarded the train. The train is now 1/4 full. How many passengers were there
on the train at first?
This time, I want to try so you can see how I think and from there I want to improve on my thinking
skills which I am lacking off.
Ok........First I take 1/2 minus from 2/5 = 1/5 (is this correct?)
Then.....I have to take the 1/4 = 1/5 + 17 (is this correct too?)
After that........actually I dont know already. Ha!
The only thing I can think of is that this is a "working backwards" problem sum.
Okay, the answer given is 136.
Thank you!

Junior
Registered: 06/17/09 Posts: 30





By: kohkah (offline) Friday, April 09 2010 @ 02:11 AM CDT



kohkah 
1/4=5/20,
1/5=4/20
therefore, 1/20=17
at first, 2/5>8/20
17*8=136

Newbie
Registered: 12/31/06 Posts: 7





By: thayal (offline) Monday, April 12 2010 @ 09:49 AM CDT



thayal 
HI could anyone help me this fraction problem?
Judy had 68 ore stickers than Jenny. After Jenny gave away 1/4 of her stickers and Judy gave away 25stickers, Jenny had 2/3 as many stickers as Judy. Ho many sticker did Judy hav at first?
Are there any model drawigs books for this type of problem sums?Please let me know

Junior
Registered: 04/18/09 Posts: 21





By: AVE (offline) Tuesday, April 13 2010 @ 12:22 AM CDT



AVE 
Hi Thayal,
sure, here is my solution although a little bit of algebraic (I can only answer systematically using algebraic method):
Let x= the original number of stickers that Judy had
y = original number of stickers that Jenny have
1st sentence:Judy had 68 ore stickers than Jenny.
x = 68 + y
Jenny gave away 1/4 of her stickers:
y  1/4y
Judy gave away 25stickers:
x25
Jenny had 2/3 as many stickers as Judy:
y  1/4y = 2/3 (x25) manipulate this eq to get y:
3/4y = 2/3 (x25)
y = 8/9 (x 25) > substitute to 1st eqn: x = 68 + y
x = 68 + 8/9 (x25)
x = (68(9) + 8x 200)/9
9x = 612 + 8x 200
9x  8x = 612  200
==================
x = 412 > answer
==================
check answer:
y = 412 68 = 344
y  1/4y = 2/3(x25)
344  1/4(344) = 2/3 (412 25)
258 = 258

Newbie
Registered: 03/08/10 Posts: 5





By: kohkah (offline) Tuesday, April 13 2010 @ 01:44 AM CDT



kohkah 
Start drawing the model from the end of the question.
Jenny is 2/3 as many as Judy
Judy 
Jenny
Judy give away 25 and Jenny give away 1/4
Judy  25<give away so we put it back
Jenny 1/4 <1/4 give away so we put it back
From here u can see 3/4 of Jenny equal to 2/3 of Judy, we have to refine the model, before that, we get the lowest common multiple of 2 and 3 which is 6
Redraw model
Judy <25>< give away 25 left 43, Judy is 68 more
JennyXXXXXXXXXX <XXXX denote 1/4 give away
From here we can see that 1 block of  is equal to 43.
Judy has 9 blocks so it will be 43*9=387, plus the 25 she give away, it yield 412!
For questions with fractions in different denominator and numerator, it will require the student to refine the blocks into smaller sizes by obtaining the lowest common multiple.
Sorry for the model is badly done. :<

Newbie
Registered: 12/31/06 Posts: 7





By: pearldyn (offline) Tuesday, April 13 2010 @ 09:19 AM CDT



pearldyn 
Quote by: kohkah1/4=5/20,
1/5=4/20
therefore, 1/20=17
at first, 2/5>8/20
17*8=136
kohkah,
why 1/20 = 17 ?
I thought 1/5 + 17 = I dont know what
oh dear, i am so stressed! I am sorry, I just didnt get it.

Junior
Registered: 06/17/09 Posts: 30





By: kohkah (offline) Wednesday, April 14 2010 @ 10:50 PM CDT



kohkah 
no worry,
lets do it slowly
from the question you know 17 passengers boarded contribute a fraction to increase the capacity from 1/5 to 1/4 .
in model drawing, draw 2 same size of blocks, one divided into 5 parts the other 4 parts.
 <> 5 blocks
 <> 4 blocks
><17 is here.
by obtaining the LCM of 4 and 5, which is 20, we are able to normalise/ convert the 1/5 and 1/4 into 4/20 and 5/20 respectively.
if memory serve me right, after obtaining the LCM, the students are to further divide the block into smaller size, subsequently they will be able to visual 1 block/unit of it is 17.
for non student, we get 1/4  1/5 = 1/20, from here we shall understand it is the 17 passengers that boarded the train.
For model involve fractions, students have to be able to get LCM, lowest common multiple, and resize the model into smaller units.

Newbie
Registered: 12/31/06 Posts: 7



