1) √40*√490
=√4*10*49*10=2*10*7=140
2) √10*√640
=√10*64*10=10*8=80
3)√2.5*√40
=√25*4=5*2=10
4)√6.4*√90
=√64*9=8*3=24
5)√18*√32
=√9*2*2*16=3*2*4=24
6)√8*√800
=√8*8*100= 8*10=80
7)√4.9*√0.9
=√49*0.1*9*0.1=7*0.1*3=2.1
8)√12.1*√0.4 =√121*0.1*4*0.1=11*0.1*2=2.2