# im totally clueless?

john and peter, ages 11 and 13, were given a job to do at 9am. working alone, john can do the job in 5 hrs, and peter in 4 hrs. at 10am they went swimming until 1:30, then came back and finished the job. at what time did they finish it?

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Lv 6

Working alone, John can do the job in 5 hrs, and Peter in 4 hrs.

=> John can do 1/5 of the work in 1 hour and

Peter can do 1/4 of the work in one hour.

So both together will do

(1/5 + 1/4) of the job in one hour (=60 minutes)

1/5 + 1/4 = (4+5)/20 = 9/20

=> 9/20 of the job in 60 minutes

9/20 ·x = 60

9x = 60·20

x = 60·20/9

x = 400/3

x = 133 1/3

This means they can both together finish the job in 133 1/3 minutes which is 2 hours, 13 minutes and 20 seconds.

They worked for 1 hour from 9am till 10am. When they came back from swimming at 1:30, they still had 1 hour, 13 minutes and 20 seconds of work to do.

Therefore they finished the job at

2:43 and 20 seconds pm

Hope this helps.

(EDIT)

OMKAR is NOT RIGHT because .23 hours does not equal 23 minutes. An hour has 60 minutes, not 100!

Working together, they need 2 hours and 13 1/3 minutes.

This is how that is determined:

John works at 5 hours per job, Peter at 4 hours per job.

So, John works at 1/5 jobs per hour and Peter and 1/4 jobs per hour.

So, to make this an algebra problem, let X equal the number of hours they need to work together to complete 1 job:

1/5 X + 1/4 X = 1 job

4/20 X + 5/20 X = 1 job

9/20 X = 1 job

therefore, X = 2 2/9 hours or 2 hours and 13 1/3 minutes

So, if they started at 9am, took 3.5 hours off in the middle, they would complete in 5 hours 43 1/3 minutes total, or at clock time of 43 1/3 minutes past 2pm.

Source(s): I have a math degree and teach college calc

John at 6:30 Peter at 5:30 I guess

HERE!, chill friend

Take a deep breadth and cool down, my answer is quite simple

Its simple,

(first you should know that we assume total work to be '1')

A/C to question,

john does the work alone in 5 hours,

so the work done by john in an hour will be 1/5

Peter does the work in 4 hours

So, the work he does in an hour is 1/4

They had started the work at 9 and stopped at 10

so they did some work for an hour

The work done by both of them in an hour,

= 1/5 +1/4

= 9/20

We know the total work is "1"

so the work that is left is 1 - 9/20

They again start working at 1.30

They can do 9/20 of the work in one hour,

So, the time they'll take to complete the left work(1- 9/20)

=(1 - 9/20)/9/20

9/20 = 0.45

= (1 - 0.45)/ 0.45

=1.2222222222222222...............

= 1.23 (approximately)

We can even express it like this:

let J be the work done by john in one hour

and P be the work done by peter in one hour

and T be the time taken to complete the remaining work

So,

(J+P) + T(J + P) = 1

=>(1 + T) ( J + P ) = 1

But we know J + P = 9/20

=>(1 + T) = 20/9

=>T= 20/9 -1

T = 1.222222222222222....

T = 1.23 (approximately)

so the answer is (1.30 + 1.23)hours

= 2.53 pm

(you also have to note that no work is done when they were swimming)

AND I AM RIGHT