求教GWD-11

bradywangs

谢谢，请指点思路。

Q8:

When positive integer x is divided by 5, the remainder is 3; and when x is divided by 7, the remainder is 4.  When positive integer y is divided by 5, the remainder is 3; and when y is divided by 7, the remainder is 4.  If x > y, which of the following must be a factor of x - y?

 

 

A.     12

B.     15

C.     20

D.     28

E.      35

Answer: E

bradywangs

明白，可是能简单告我，同余定理在此题中如何用?我知道这个定理，但不太会用。