Answer: $6.25
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Work Shown:
x = some positive real number, ie, x > 0
A = amount Annie chips in = 3x
B = amount Billy chips in = 5x
C = amount Chuck chips in = 4x
Amounts are in dollars.
Note the ratio A:B:C turns into 3x:5x:4x which simplifies to 3:5:4 when we divide all three parts by the GCF x.
The total amount collected was $15, meaning we can say
A+B+C = 15
3x+5x+4x = 15
12x = 15
x = 15/12
x = (3*5)/(3*4)
x = 5/4
x = 1.25
Use this x value to find the values of A, B, and C
A = 3x = 3*1.25 = 3.75
B = 5x = 5*1.25 = 6.25
C = 4x = 4*1.25 = 5
We see that Billy contributed $6.25
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As a way to check, we would do the following
A+B+C = 3.75+6.25+5 = 15
So the answer is confirmed.
Also note that the ratio 3.75:6.25:5 reduces to 3:5:4 when you divide all parts by 1.25; this fact may be more obvious if you wrote the ratio in this form
3*1.25 : 5*1.25 : 4*1.25
which shows 1.25 popping up three times