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 Levi's dad to wash the car by himself

Answer 1

Answer:

1 hour and 40 minutes

Step-by-step explanation:

Answer 2

Answer:

Levi's dad takes 1.67 hours to wash the car by himself

Step-by-step explanation:

* Lets explain how to solve the problem

- Levi takes 2.5 hours to wash his dad's car alone

- Levi and his dad take 1 hour to wash the dad's car together

∵ Levi takes 2.5 hours to wash the car alone

∴ The rate of Levi is 1/2.5 car/hr

∵ His dad takes x hours to wash the car alone

∴ The rate of his dad is 1/x car/hr

∵ They working together for 1 hour to wash the car

- The equation of the work is rate of Levi × t + rate of his dad × t = 1

∵ t is the time of working together

∵ t = 1 hour

∴ $\frac{1}{2.5}(1)+\frac{1}{x}(1)=1========\frac{1}{2.5}+\frac{1}{x}=1$

- Multiply both sides by 2.5x to cancel the denominators

∵ $\frac{1}{2.5}(2.5x)=x=====\frac{1}{x}(2.5x)=2.5$

∵ 1 × (2.5x) = 2.5x

∴ x + 2.5 = 2.5x

- Subtract x from both sides

∴ 2.5 = 1.5x

- Divide both sides by 1.5

∴ x = 5/3 ≅ 1.67

∵ x is the the time of his dad to wash the car alone

∴ Levi's dad takes 1.67 hours to wash the car by himself