Solution: There are big monk X and little monk Y. ..

According to the question, x+y =100-

3x+y/3= 100——②

②×3, get

9x+y=300——③

③-①. Obtain

8x=200

x=25

Substitute x=25 into ①, and you get

25+y= 100

y=75

∴x=25

y=75

A: There are 25 big monks and 75 small monks.