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Wednesday, June 28 2017 @ 07:23 AM CDT
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By: Super (offline)  Saturday, February 05 2011 @ 09:24 AM CST (Read 1785 times)  
Super

Hi,

Need help on the following maths question. Appreciate your assistance. Thanks in advance.

The ratio of $5-notes to 20-cents coins in Mr Tan's counter was 19:5. Mr Tan exchanged 15 of his $5-notes for some 20-cents coins. The ratio of the $5-notes to 20-cent coins then became 1:5. What was the total value of $5-notes and 20-cent coins at first?

Thanks.

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By: peterb5 (offline)  Thursday, February 10 2011 @ 11:51 PM CST  
peterb5

It is quite a common type of question. You must remember that the total value of the money will not change. Thus you need to change the ratio to a ratio of value rather than a ratio of the number of notes and coins.


Before After

$5 : 20c $5 : 20c
number 19:5 1:5
value (converted to cents) 9500:100 500:100
simplify the ratio 95 : 1 5 : 1

as the total value must stay the same therefor find the lowest common multiple of 96 and 6 (96)
therefore we multiply the after ratio by 16
95 : 1 80 : 16
as you can see the $5 notes goes down by 15 units and 20c goes up by 15 units therefore

15 units -> 15 x 5 = 75
1 unit -> 75 divided by 15 = 5

96 units is 96 x 5 = 480

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