1) 61²-39²=(61-39)(61+39)=22*100=2200
2) 45²-55²=(45-55)(45+55)=-10*100=-1000
3) 13.6²-3.6²=(13.6-3.6)(13.6+3.6)=10*17.2=172
4) 5.8²-94.2²=(5.8-94.2)(5.8+94.2)=-88.4*100=-8840
5) (1 3/5)²-(2/5)²=(1 3/5-2/5)(1 3/5+2/5)=1.2*2=2.4
6) (3 5/8)²-(1 3/8)²=(3 5/8-1 3/8)(3 5/8+1 3/8)=2.25*5=11.25