Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$0.4$
We know that probability$=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}.$ We have $100$ households in total. There are $35+5=40$ households whose income is less than $\$20,000$. Thus,$P=\frac{40}{100}=0.4\$