There are approximately 1.2×10 to the eighth household in the US if the average household uses 400 gallons of water each day what is the total number of gallons of water used by households in the US each day

4.8×10^10 gallons
Step-by-step explanation:
The desired number is the product of the number of households and the volume of water used by each:
(1.2×10^8 households)(4×10^2 gal/day/household) = (1.2·4 × 10^(8+2)) gal/day
= 4.8×10^10 gal/day