Easiest way of mathematical question to solve without calculator.

Question

X² of large number

Answer 1

25^2 = 625

if the number ends in 5

take the ten's digit and add 1, to get 3

2x3 =6, then combine that with 5^2 =25 to get 625

125^2 = 15625

12x13=156 from your 3rd grade multiplication tables you memorized long ago

but may have forgotten. You must remember 12x12 =144, (it's even sort of in the Book of Revelation, as JW's remind us), then just add another 12 to get 156

combine it with 25 to get 15625

1005^2 =1010025

100x101 = 10100, just add 2 zeroes

then combine that with 25 to get 1010025

other huge numbers you may just want to estimate by rounding approximations

60123 = about 60000

60000 times 60000 = 3600000000

6 with 4 zeros times 6 with 4 zeros = 36 with 8 zeros (4+4)

you can do it all in your head, no calculator, no paper required