Answer:
2 hours 15 minutes
2.25 hours.
Step-by-step explanation:
Let Maria's time by herself = x minutes
Let Miguel's time by himself = 2x minutes
You have to be careful how you set this equation up. Start with the right. The 1 represents the Job to be done. It takes 90 minutes.
The left hand side = 1/x which is the amount of time Maria (x) takes to do the job by herself. She doesn't do the job by herself.
Miguel helps her, so the portion he does is represented by 1/2x. Because he's helping, her time is cut back; he's doing some of the work.
1/x + 1/(2x) = 1/90 minutes
(2 + 1)/(2x) = 1/90 minutes
3/(2x) = 1/90 minutes
270 = 2x
x = 135 minutes.
It would take her 135 minutes to do the windows alone. That's 2 hours and 15 minutes.
