At a particular gas station, gas costs $3.29 per gallon, but if you buy a $4 car wash gas costs $2.89 per gallon. When is it cheaper to buy the carwash?

Buying $4 car wash

Step-by-step explanation:

When one buys $4 gas, the cost per gallon is $2.89 but if the one spends less than $4, the cost per gallon is $3.29. The reduction in cost when one buys gas of $4 and above is the benefit of bulk purchase. The difference in prices of these two cases will be $3.29-$2.89=$0.4

Therefore, going for gas of $4 is advantageous since one saves $0.4 per gallon.