What is the formula used?

Question

I used to know what formula to use for a problem like this, but cannot remember anymore.

If Sam can do a job in 4 days that Lisa can do in 6 days and Tom can do in 2 days, how long would the job take if Sam, Lisa, and Tom worked together to complete it?

Any help would be appreciated.

Anonymous · Accepted Answer

first u need to find how much each person works in 1 day.
here Sam does 1/4 th of the job in one day.
lisa does 1/6 th of the job and tom does 1/2 of the job in one day.

so in one day together they can do 1/4+1/6+1/2 = 11/12 of the job in one day.
so they can do the whole job in 12/11 days = 1 1/11 days

Captain Matticus, LandPiratesInc · Answer

Sam does the job in 4 days, which means he does 1/4 of the job in a day
Lisa does the job in 6 days, which means she does 1/6 of the job in a day
Tom does the job in 2 days, which means he does 1/2 of the job in a day

1/4 + 1/6 + 1/2 =>
3/12 + 2/12 + 6/12 =>
11/12

Working together, 11/12 of the job is completed in 1 day

1 / (11/12) => 12/11

It will take them 12/11 days to complete the job

Marwan El-mounajjed · Answer

I'm the best in my college so i can help you
sam does 25% of the job in a day
lisa does it 16.67%=100%/6
tom does it 50%
adding them= 1100%/12
let x be the number of days
we need 100% so
1100%*x/12=100%
the answer is 12/11 days 
1 day and 7854.5 seconds=1 day, 2 hours,10 minutes and 54 seconds

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What is the formula used?

3 Answers