·
Time and Work problems are the prime example
of indirect proportion. As we all know that if number of persons are increased
then time taken to complete a given work would decrease. In indirect proportion
when one variable is increase other would automatically decreased and
vice-versa.

·
In this chapter we will all types of problems
asked in examination one by one through examples.

**Points to Remember:**

·
Inverse of the work done in one will give the
total time require to complete that work. Hence our primary aim would be to
find out work done in one day.

·
If A is twice efficient as B than the ratio
of their work done will A: B = 2:1 and so on.

__Example:__

A take 5 days to complete a job and B takes 10
days to complete the same job. In how much time they will complete the job
together?

__Explanation:__

Work
done by A in one day = 1/5

Work
done by B in one day = 1/10

Work
done by both together in one day = 1/5 + 1/10

= 3/10

Since
inverse of work one in one day gives total time to complete the given job

Hence,
total time taken to complete the job when working together = 10/3 = 3.333 Days.

__Example:__

**A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is ?**

__Explanation:__

Work
done by A in one day = 1/15

Work
done by B in one day = 1/20

One
done in one day when working together = 1/15 + 1/20

=
7/60

Since
they work together for 4 days ,

Work
done in 4 days when working together = 4×7/60

=
7/15

Fraction
of work left = 1- work completed

= 1- 7/15

= 8/15

__Example:__

**A is twice as good a workman as B and together they finish a piece of work in 14 days. A alone can finish the work in?**

Explanation:

Since A is Twice good as B, Hence
ratio of work done of A & B = 2:1

Let, Work done by A alone in one day
= x

Therefore, work done by B alone in
one day would be = x/2

Work done in one day when working
together = x + x/2

= 3x/2

Time taken in completing the work =
2/3x = 14(given)

X=1/21

A alone can finish the work in 21
Days.

__Example:__

A and B can do
piece of work in 12 days; B and C in 15 days; C and A in 20 days. A alone can
do the work in?

Explanation:

One day work of

A+B =1/12

B+C = 1/15

C+A = 1/20

Formula to get one
day work of

**A = ½ [ one day work of (A+B) +one day work of (A+C) - one day work of (B+C) ]****=**

^{1}/_{2 }**[**

^{1}/_{12 }+^{1}/_{15 -}^{1}/_{20 }]**=**

^{1}/_{30}
Hence A alone can finish work in 30 days

__Example:__

A and B can do a work in 8 days, B and C can
do the same work in 12 days. A, B and C together can finish it in 6 days. A and
C together will do it in ?

__Explanation:__

One day work
of

A+B
=

^{1}/_{8}……..(1)
B+C
=

^{1}/_{12 …….}(2)
A+B+C =

^{1}/_{6 }…….(3)_{ }

_{ }2×Eqn(1) – [Eqn (2) + Eqn (1)]

This will give work done in one day by A
& C together =

^{1}/_{8}
Hence, Time taken by A & C to complete
the work = 8 days.