Question

A, B and C can complete a work in 12, 15and 20 days, respectively. How long will they take to do it working together?​

Answer 1

Answer:

5

Step-by-step explanation:

A can do a piece of work in 12 days

B can do the same work in 15 days

C can do the same work in 20 days

∴ A’s 1 day’s work = 1/12

B’s 1 day’s work = 1/15

C’s 1 day’s work = 1/20

∴ (A + B + C)’s together 1 day’s work = 1/12 + 1/15 + 1/20

= (5 + 4 + 3)/60

= 12/60

= 1/5

∴ They can do the work in 5 days.

Answer 2

These types of problem can be solved by considering Rate at which work is done because for work to be done Time can’t be added as it is inversely proportional ,it is Rate which should be added.

Since Rate is inversely proportional to Time taken by a person.

So we can say for X amount of work their respective Rates are :

A =X/12

B=X/15

C=X/20

So their combined Rates are considered when they do work together.

Rate=X/12+X/15+X/20=X/5.

So if they work together it will take a total of 5 days to complete same amount of work.

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