Question

washing his dad's car alone eight year old Levi takes 2.5 hours. if his dad helps him, then it takes 1 hour . how long does it take the levi's dad to wash the car by himself?

Answer 1

1 hour and 40 mins

Explanation:

Levi takes 2.5 hours to wash his dads car he completes 2/5 (2 over 5 fraction) of the job per hour

His dad take some time (t) to do the same job and completes 1/t (fraction)

Working together they completes the job in 1 hour

So

2/5 + 1/t = 1/1

Multiply each side by the LCD 5t

5t (2/5+1/t)=5t(1/1)

Simplify and solve

2t+5=5t

2t+5-2t=5t-2t

5=3t

T=5/3

Multiply the fraction by 60 to convert time into mins

T=1 hour + 2/3(60mins)

So

t=1 hour and 40 mins

Levi’s dad takes 1 hour and 40 mins to wash his car alone

Answer 2

It will take Levi's dad 1.67 hours to wash the car alone.

Explanation:

Time taken by Levi to wash car alone = 2.5 hours

Time taken by Levi and his father together = 1 hour

Let,

x be the time taken by Levi's dad.

Levi will contribute 1/2.5 hours and his dad will contribute 1/x to wash the car together.

`(1)/(2.5)+(1)/(x)=1\\\\(x+2.5)/(2.5x)=1\\\\x+2.5=2.5x\\\\2.5=2.5x-x\\\\2.5=1.5x\\\\1.5x=2.5`

Dividing both sides by 1.5

`(1.5x)/(1.5)=(2.5)/(1.5)\\x=1.67`

It will take Levi's dad 1.67 hours to wash the car alone.