Word problem 2

[debbie29]

One more word problem question:

Working together Linda and Jim can clean the windows of their house in 3 hours and 36 hrs. Linda can clean all the windows by herself in 7 hours. How long will it take Jim to clean the windows by himself?

This is what I have so far:

Familiarize:

Together can do the job in 3.36 minutes
Linda by herself in 7 hours
Jim= ?

Let t= the time it takes Jim to do the job working alone. In 1 hour Linda (A) can do 1/7 of the job and Jim (B) can do 1/t of the job.

Then, in 3.6/hr A can do 3.6 (1/7) of the job and B can do 3.6 (1/t) of the job. Adding the fractional parts= the entire job repersented by 1.

Translate:

3.6 (1/ 1/7) + 3.6 (1/t)= 1
Multiply by LCM (1/7t)
1/7t ( 3.6/ 1/7t + 3.6/t) = 1/7t (1)

3.6t + 0.514 = 1/7 3.6* 0.1428= 0.514, 0.1428= 1/7
0.514=3.22 3.6-1/7= 3.22
0.159= T
And I go on to calculate the end answer and its wrong! Am I making a mistake somewhere that I can't see????

 

[stapel]

Linda and Jim can clean the windows of their house in 3 hours and 36 hrs.

Three hours? Or thirty-six hours?

Together can do the job in 3.36 minutes

Where did this under-four-minute time come from?

I am going to guess that the exercise is as follows:

Working together, Linda and Jim can clean the windows in three hours and thirty-six minutes. Linda can clean the windows by herself in seven hours. How long would it take Jim to clean the windows by himself?

Convert the times to rates. If Linda can do the whole job in seven hours, how much can she do in one hour? If they can do the whole job together in 3.6 hours (thirty-six minutes being 3/5 of an hour), then how much can they do in one hour?

. . . . .time to complete:
. . . . .Linda: 7
. . . . .Jim: j
. . . . .together: 3.6

. . . . .completed per time unit:
. . . . .Linda: 1/7
. . . . .Jim: 1/j
. . . . .together: 1/3.6 = 5/18

. . . . .(what Linda does in one hour) and
. . . . . . . .(what Jim does in one hour)
. . . . . . . . . . .equals (what they do together in one hour)

Translate the sentence above into an equation, and solve.

Eliz.

 

[debbie29]

oops! sorry- 3 hours, 36 minutes!

I'll try your suggestions-- thanks!!

D