Ellen drove 357.9 miles. her car gets about 21 miles per gallon. which is the best estimate of how many gallons of gas ellen used?

When looking for an estimate, you have to round your numbers 21 rounded would become 20 and 357.9 would become 360. So next you would divide the numbers.

360 ÷ 20 =  18

So, Ellen would have used approximately 18 gallons of gas.

Hope this helps you. :-) 

10% of increase is the final answer! : )