we know that Dad and Junior can wash the car together in 40 minutes, and Junior can do it by himself in 70 minutes. To find out how long it would take Dad to do it by himself, we can use the concept of work rate. Since Dad and Junior working together can finish the job in 40 minutes, their combined work rate is 1/40. If we let Dad's work rate be x, then Junior's work rate would be 1/70. To find Dad's work rate, we subtract Junior's work rate from the combined work rate: 1/40 - 1/70 = 3/280. This means that Dad's work rate is 3/280 of the job per minute. To find out how long it would take Dad to do the job by himself, we can use the formula: time = 1 / work rate. Plugging in Dad's work rate, we get: time = 1 / (3/280) = 280/3 minutes. So, it would take Dad approximately 93.33 minutes to wash the car by himself.
