4)(2 7/10-1 8/15)²=(2 21/30-1 16/30)²=(1 1/6)²=(7/6)²=49/36
49/36*9/14=7/8
3) (3 1/3)²=(10/3)²=100/9=11 1/9
2 13/16*2 2/5=45/16*12/5=27/4=6 3/4
11 1/9-6 3/4=11 4/36-6 27/36=5-16/36=4 20/36=4 5/9
4)(5/12+13/20)²=(25/60+39/60)²=(64/60)²=(16/15)²=256/225
256/225*1 13/32=256/225*45/32=8/5=1 3/5