Mary can paint a house in 4 hours. John can paint a house in 6 hours. How long will it take for them to paint a house together
Make this chart:
number of number of rate
houses hours in
painted required houses/hour
Mary painting alone
John painting alone
Both painting together
Let x = the number of hours it will take both painting together.
Fill that in and the number of hours required for Mary and John, 4 and
6 respectively.
number of number of rate
houses hours in
painted required houses/hour
Mary painting alone 4
John painting alone 6
Both painting together x
In each case 1 house is painted. We fill in 1 for the number of houses
painted in each case:
number of number of rate
houses hours in
painted required houses/hour
Mary painting alone 1 4
John painting alone 1 6
Both painting together 1 x
Fill in the rates in houses/hour bu dividing the number of houses
by the number of hours required.
number of number of rate
houses hours in
painted required houses/hour
Mary painting alone 1 4 1/4
John painting alone 1 6 1/6
Both painting together 1 x 1/x
The equation comes from:
+ =
+ =
Solve that and get x = 2.4 hours or 2 hours 24 minutes
Edwin