## Precalculus (10th Edition)

$0.6$
We know that $\text{probability}=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}=\frac{n(E)}{n(S)}.$ Hence here because we have $n(E)=30+20+10=60$ houses with an income at least $20000\$$, in total we have$n(S)=100$houses, therefore$\text{probability}=\frac{60}{100}=0.6.\$