The ratio of the number of one dollar coins in a box was 3:4.six one dollar coins were removed & some fifty cent coins of the same amount were added.the ratio of the number of one dollar coins to the number of fifty cent coins then became 1:3.what was the total amount of money in the box?

5 answers

if there were x 50-cent coins and y dollar coins, then if 6 dollars were replaced with 12 halves,

x/y = 3/4
(x-6)/(y+12) = 1/3

clearing the fractions, we have

4x = 3y
3(x-6) = y+12

4x-3y = 0
3x-y = 30

now we see that y=3x-30, so

4x-3(3x-30) = 0
4x-9x+90 = 0
5x = 90
x = 18

So, there were 18 dollars and 24 halves.

After the replacements, there were 12 dollars and 36 halves.

I expect you can figure out how much money that was.
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