Which equation?

Question

Which of the following equations are equivalent to 

(4 x 10^-7) + (5 x 10^-7) ?

 

equations: 9 x 20^-14

                90^-7

                9 x 10^-7

                 9 x 20^-7

Answer 1

When adding two numbers in scientific notation (each must have the same power of ten!), only the number (not the power of ten) is added.

 

4 x 10^-7 + 5 x 10^-7

9 x 10^-7