GMAT Quantitative Reasoning Practice Test 1

If at least one member must be a woman, the committee will have either one woman and two men or two women and one man. Use combinations because the order does not matter.
Choosing one woman and two men:
$2{\mathit{C}}_1\times 4{\mathit{C}}_2=\frac{2}{1}\times \frac{4\times 3}{2\times 1}=\frac{24}{2}=12$
Choosing two women and one man:
$2{\mathit{C}}_2\times 4{\mathit{C}}_1=\frac{2\times 1}{2\times 1}=\frac{4}{1}=\frac{8}{2}=4$
Since both situations would satisfy the requirement that at least one member is a woman, add the combinations.

$12+4=16$ total committees.