Chapter R - Section R.2 - Operations on Real Numbers - R.2 Exercises - Page 21: 100

$-\frac{21}{100}$

$\frac{9}{20}(-\frac{7}{15})=\frac{9\times-7}{20\times15}=\frac{-63}{300}=-\frac{63}{300}$ $-\frac{63}{300}=-\frac{63\div3}{300\div3}=-\frac{21}{100}$ The two numbers being multiplied together have different signs, so so the resulting product is negative.