I got an answer for a problem but I want to know why a 7 was added to the end of it pls help. Question:

In order to have the answer, 3.487×10^-5, you have to make the power of 10 into -5 :

7×10^-8 = 0.007×10^-5

e.g.

1×10^-2 = 0.01

1×10^-4 = 0.01×10^-2

(take note: when the power is negative, you have to move to the left)

Then you can solve it :

0.007×10^-5 + 3.48×10^-5

= 10^-5(0.007 + 3.48)

= 10^-5(3.487)

= 3.487×10^-5