Mary has boxes with Christmas balls of two colors: orange and blue. Each orange box contains a fixed number of orange balls, and each blue box contains a fixed number of blue balls. If Mary substituted one orange casino online box for one additional blue box, the total number of balls would decrease by 15, and the difference between the total number of orange balls and the total number of blue balls would increase by 65. How many Christmas balls are there in each blue box?

A. 20

B. 25

C. 35

D. 40

E. 50

B. 25

The answer is B.

Let the number of orange balls in each box be o, the number of such boxes – x; the number of blue balls in each box – b, the number of such boxes – y.

Then we have two equasions:

1) ox + by – (o(x-1) + b(y+1)) = 15

2) ox – by – (o(x-1) – b(y+1)) = 65

After simplifying and substructing (2) from (1) we have -2b=-50.

Thus, b=25, and that is the answer.

40