118/121*13
=13*(1-3/121)
=13*1-13*3/121
=13-39/121
=12+1-39/121
=13+82/121
=13又121分之82
2/25*126
=（125+1)*2/25
=125*2/25+1*2/25
=10+2/25
=10又25分之2