P can do a work in 10 days Q n 12 R in 15. if they work together how many days wud they take to finish?

Question

THE OPTIONS ARE: 2, 3, 4, 5. PLEASE EXPLAIN HOW U GOT THE ANSWER

Answer 1

let the total no of days =x
let the total amount of work=w
p*10days=w
so p=w/10
similarly
q=w/12
r=w/15

w/10+w/12+w/15=w/x
w(6+5+4)/60=w/x
15/60=1/x
1/4=1/x
so x=4days

Answer 2

Answer: 4 days

P can do 1/10th job a day
Q can do 1/12th job a day
R can do 1/15th job a day.

1/10+1/12+1/15 (need common demoninator which is 60)

6/60+5/60+4/60= 15/60
Together they can do 15/60 th of the job a day.

So, 60 divided by 15 = # of days needed , which is 4.

Answer 3

P can do a work in 10 days
divide this job equaly for ten days.
In one day P can finish 1/10 of the job.

Therefore
1/10+1/12+1/15=1/x

x=?

1/x=15/60

x=4 days

Answer 4

P will do 1/10 of the work in 1 day
Q will do 1/12
R will do 1/15

add them all up and u will get 1/4
thus they need 4 days!(:

Answer 5

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Answer 6

Their total work rate is the reciprocal of the sum of their individual work rate reciprocals. So their total work rate is
1/(1/10 + 1/12 + 1/15) = 4 days.


Doug

Answer 7

Why don't you do your own homework?
This question is not difficult.