#### Answer

There are $2.88\times 10^{13}$ red blood cells in the body of a 180-pound person.

#### Work Step by Step

$180\: pounds \times\frac{ 3.2 \times 10^{4}\:microliters\: of\: blood}{pound} \times \frac{5 \times10^{6}\: red\: blood\: cells}{microliter\: of\: blood}$
Recall the multiplication of scientific notation: $(a \times 10^{n})(b \times 10^{m}) = (a \times b) \times 10^{n+m}$
Thus, the whole equation can be written as:
$$180 [ (3.2 \times 10^{4}) \times(5 \times10^{6})]$$ $$=180[(3.2\times5)\times 10^{4+6}]$$ $$=180[16\times 10^{10}]$$ $$=2880\times 10^{10}$$
Since the numerical factor, $a$, should be a number between 1 and 10, then this could be rewritten as:
$$2.88\times 10^{13}$$