Question

You promised your parents that you would wash the family car. You have not started the job and they are due home in 20 minutes. You can wash the car in 45 minutes and your sister claims she can do it in 30 minutes. If you were together, how long will it take to do the job? Will this give you enough time before your parents return?

Answer 1

Step-by-step explanation: x[(1/45) + (1/30)] = 1

x[(30 + 45) / 1350] = 1

x(75/1350) = 1

x = 1350 / 75

x = 18 minutes

if it takes you 45 minutes to wash one car, then you wash 1/45 of the car in one minute

if it takes your sister 30 minutes to wash one car, then she washes 1/30 of the car in one minute

together you wash

(1/45) + (1/30) = 75/1350 or 1/18 of the car in one minute

let x = number of minutes

x(1/18) = 1

it equals one because that is the number of cars being washed

x = 18

it will take 18 minutes with the two of you working together to wash one car

Hope I helped