3-1又7分之2-7分之5
=3-(1+2/7+5/7)
=3-2
=1;
8分之7+4分之3+1又8分之1+4分之1
=(7/8+1+1/8)+(3/4+1/4)
=2+1
=3;
28分之25-(7分之3+14分之5)
=25/28-12/28-10/28
=3/28;
15分之8-(5分1-6分之1)
=8/15-1/30
=16/30-1/30
=15/30
=1/2;
9分之7+2分之1+9分之2
=(7/9+2/9)+1/2
=1+1/2
=3/2;
20分之13+5分之2-10之7
=13/20+8/20-14/20
=7/20;