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Chapter - 12

Time and Work

Three main factors of Time and Work

There is a definite relationship between Time and Work. In this concept, there are only three factors: Time taken to complete a certain job

Unit of work done

Number of persons doing the job

There is a mental relationship between these three, discussed as follows:

Work done (W) = Number of days (Time taken) (T or D) × Number of men (M)

W = D × M

Some basic points

More number of men can do more work i.e. both are directly proportional

More number of men take less time to complete certain job i.e. both are inversely proportional

By summarizing, we get = ×

Let us start solving some examples:

Example 1: 10 men can cut 8 trees in 16 days. In how many days can 6 men cut 10 trees?

Solution: This is a very simple example. You are given:

W1 = 8

W2 = 10

M1 = 10

M2 = 6

D1 = 16

D2 = ?

Using formula, = ×

= ×

⇒D2 = 33.3

Concept of efficiency

This means, "How much work one person can do in one day (expressed in percentage)" For example: A person can do a job in 2 days

⇒ He can do 50% work in one day

Therefore, his efficiency will be 50%

Just a 2-step concept

This concept involves two steps to calculate efficiency: Convert into fraction i.e. per day work

Multiply with 100 i.e. convert into percentage

Chapter - 12

Time and Work

Three main factors of Time and Work

There is a definite relationship between Time and Work. In this concept, there are only three factors: Time taken to complete a certain job

Unit of work done

Number of persons doing the job

There is a mental relationship between these three, discussed as follows:

Work done (W) = Number of days (Time taken) (T or D) × Number of men (M)

W = D × M

Some basic points

More number of men can do more work i.e. both are directly proportional

More number of men take less time to complete certain job i.e. both are inversely proportional

By summarizing, we get = ×

Let us start solving some examples:

Example 1: 10 men can cut 8 trees in 16 days. In how many days can 6 men cut 10 trees?

Solution: This is a very simple example. You are given:

W1 = 8

W2 = 10

M1 = 10

M2 = 6

D1 = 16

D2 = ?

Using formula, = ×

= ×

⇒D2 = 33.3

Concept of efficiency

This means, "How much work one person can do in one day (expressed in percentage)" For example: A person can do a job in 2 days

⇒ He can do 50% work in one day

Therefore, his efficiency will be 50%

Just a 2-step concept

This concept involves two steps to calculate efficiency: Convert into fraction i.e. per day work

Multiply with 100 i.e. convert into percentage