15－5÷12－7/12
=15－5/12－7/12
=15－(5/12+7/12)
=15-1
=14
2－1/4－1/3－3/4
=2－1/4－3/4－1/3
=2-(1/4+3/4)－1/3
=2-1-1/3
=1-1/3
=2/3
5/8－（5/8－1/2）
=5/8-5/8+1/2
=1/2
1/5×37%＋4/5×37%
=(1/5＋4/5)×37%
=37%
1/6÷11/24－3/8×4/11
=1/6*24/11－3/8×4/11
=4/11－3/8×4/11
=4/11(1－3/8)
=4/11*5/8
=5/22
68－7.5＋32－2.5
=68＋32－7.5－2.5
=100－(7.5+2.5)
=100-10
=90