Bài giải:

S.AMN = $\frac{2}{3}$ x S.NAB = $\frac{2}{3}$x$\frac{1}{3}$ x S.ABC = $\frac{2}{9}$ x S.ABC = 40 ( cm²)

S.BMQ = $\frac{1}{2}$x S.MBC = $\frac{1}{2}$x$\frac{1}{3}$x S.ABC = $\frac{1}{6}$ x S.ABC = 30 (cm²)

S.CPQ = $\frac{1}{2}$x S.PBC = $\frac{1}{2}$x$\frac{1}{3}$x S.ABC = $\frac{1}{6}$ x S.ABC = 30 (cm²)

S.MNPQ = 180 – 40 – 30 – 30 = 80 (cm²)

    Đáp số: 80cm²