Fund Raiser

I have raised $4978 for charity.

  • The men benefactors have contributed an average of $67.
  • The women benefactors have contributed an average of $59.

How many benefactors are there?


The answer is 78.

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1 solution

Let x x be the number of men and y y the number of women. We can set up a diophantine equation: 67 x + 59 y = 4978 67x + 59y = 4978

By Euclidean algorithm, we can calculate:

67 = 59 + 8 67= 59 + 8

59 = 8 7 + 3 59 = 8•7+3

8 = 3 2 + 2 8= 3•2+2

3 = 2 1 + 1 3= 2•1+1

Then 1 = ( 59 8 7 ) ( 8 3 2 ) = 59 25 22 67 1= ( 59-8•7)-(8-3•2)= 59•25-22•67

Thus, 4978 = 59 ( 25 4978 ) 67 ( 22 4978 ) 4978= 59(25•4978)-67(22•4978) .

That is, x 0 = 22 4978 x_{0} = -22•4978 and y 0 = 25 4978 y_{0}=25•4978 .

Since 67 67 and 59 59 are coprime, x = x 0 + 59 n > 0 x= x_{0}+59n >0 and y = y 0 67 n > 0 y=y_{0}-67n>0 .

Hence, 25 4978 67 > n > 22 4978 59 \dfrac{25•4978}{67}>n>\dfrac{22•4978}{59} .

Only n = 1857 n=1857 works.

As a result, x = 22 4978 + 59 1857 = 47 x=-22•4978+59•1857=47 .

y = 25 4978 67 1857 = 31 y=25•4978-67•1857=31 .

Finally, the total benefactors= 47 + 31 = 78 47+31=\boxed{78} .

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