**1) ** A committee consisting of 3 girls and 4 boys can be formed in ^{1}C_{3}×^{9}C_{4} ways

⇒^{4}C_{1}×^{9}C_{4}

⇒4/1×9×8×7×6/1.2.3.4

⇒504 ways

**2) **Since, the committee requires 7 members and it must have at least 3 girls means the committee can consist 3 or more number of girls.

This can be done in two ways, i.e., select 3 girls from 4 or all the 4 girls.

By the principles of combination, we can select 4 boys from 9 and 3 girls from the 4 or also 3 boys and 4 girls.

This can be computed as total (9C4 * 4C3) + (9C3 * 4C4) ways