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Monday, August 21 2017 @ 01:43 AM CDT
 Forum Index >  Test Paper Related >  Primary 5 Matters
 problem sums for p5
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By: Geeta (offline)  Sunday, October 30 2011 @ 01:06 AM CDT (Read 1818 times)  
Geeta

A coin box contained some 20 cents and 50 cents coins in the ratio 4:5. When 16 50 cents coins where taken out and replaced by some 20 cents coins the ratio then became 8:7. T he total value of 20 cents coins added was the same as the total value of the 50 cents coin taken out. Find the sum of money in the coin box? Surprised!

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By: sokechan (offline)  Sunday, October 30 2011 @ 01:36 AM CDT  
sokechan

20 : 50 20 : 50
4 : 5 28 : 40
+40 -16 ----> +280 -80
------------ --------------
8 : 7 56 : 56

12 u = 280 + 80 = 360
28 u = 840
40 u = 1200
840 * 0.20 = 168
1200 * 0.50 = 600
600 + 168 = 768

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By: Geeta (offline)  Sunday, October 30 2011 @ 03:28 AM CDT  
Geeta

but the answer is $112.20

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By: sokechan (offline)  Sunday, October 30 2011 @ 03:58 AM CDT  
sokechan

20 : 50
4 : 5
+40 -16
------------
8 : 7

20 : 50
+280 -128
----------------
56 : 56

12 u = 280 + 128 = 408
4 u = 136
5 u = 170
136 * 0.20 = 27.2
170 * 0.50 = 85
27.2 + 85 = 112.2

Sorry. Some mistakes here and there.

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By: Geeta (offline)  Sunday, October 30 2011 @ 04:40 AM CDT  
Geeta

how did u get 280 and 128 can you please explain me in detail..? Thanks again...

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By: sokechan (offline)  Sunday, October 30 2011 @ 06:04 AM CDT  
sokechan

I try to make the units in the end the same so the 20 cents section is multiplied by 7, and the 50 cents section is multiplied by 8.
40 * 7 = 280
16 * 8 = 128

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By: NQS (offline)  Sunday, October 30 2011 @ 07:57 AM CDT  
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Quote by: Geeta

how did u get 280 and 128 can you please explain me in detail..? Thanks again...



7 x 40=280
16 x 8=128

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By: NQS (offline)  Sunday, October 30 2011 @ 08:04 AM CDT  
NQS

Quote by: sokechan

20 : 50
4 : 5
+40 -16
------------
8 : 7

20 : 50
+280 -128
----------------
56 : 56

12 u = 280 + 128 = 408
4 u = 136
5 u = 170
136 * 0.20 = 27.2
170 * 0.50 = 85
27.2 + 85 = 112.2

Sorry. Some mistakes here and there.





They call it the cross multiplication method

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By: Geeta (offline)  Monday, October 31 2011 @ 01:18 AM CDT  
Geeta

Thanks....

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