Question 741813
<pre>
(2.5×10<sup>8</sup>)(8×10<sup>7</sup>)

Multiply the 2.5×8 and get 20. 
Add the exponents 8+7 and get 15

So that becomes

20×10<sup>15</sup>

However, that is not in scientific notation
because the 20 is not between 1 and 10.  So
we get 20 in scientific notation as 2×10<sup>1</sup>,
Then we replace the 20 by 2×10<sup>1</sup>:

2×10<sup>1</sup>×10<sup>15</sup>

and we add the exponents and end up with

2×10<sup>16</sup>

Edwin</pre>