Verified answer

1   = (15+0.2)(15-0.2) = 15^2-0.2^2 = 225-0.04 = 224.96

2      =(20-0.1)(20+0.1)=400-0.01=399.99

3     = (4+0.01)(4-0.01)=16-0.0001=15.9999

4       =(30-0.2)(30+0.2) =900-0.04=899.96

5     =(86-14)(86+14)=72*100=7200

6    =(328-172)(328+172) = 156*500=78000

7      =(2 3/4- 1 1/4)(2 3/4+ 1 1/4) = 1.5*4 = 6

8      =(7 1/5-2 1/5)(7 1/5+2 1/5) = 5*9.4 = 47