Question

9.99x10 ^-2 + 1.11 × 10^-2 i dont have the same scientific calculator as the one from school. Would like to verify my math is correct

Answer 1

The answer should not depend on which machine or which pencil you use to
find it.  If you work a problem two different ways and get two different answers,
then at least one of them is wrong, and there's a pretty good chance that both
of them are.

(9.99 of anything) + (1.11 of the same thing) = 11.1 of them

9.99 (x 10^-2) + 1.11 (x 10^-2) = 11.1 (x 10^-2) .

Can we do any more with that ?

10^-2  =  1 / 10^2  =  1 / 100 .

11.1 x 10^-2  =  11.1 / 100  =  0.111