Question

If 18 birds can make 18 nests in 18 days, then how much time will be taken by one bird to make a nest?

Answer 1

Answer:

18 days

Step-by-step explanation:

18 birds make the nest in 18 days,

When it is put together, lets calculate for one bird each,

Hence, one bird would take to build 18 nests in 18x18 days

Therefore one bird would take to build 1 nest = (18x18)/18

                                       = 18 days

Therefore, 1 bird would take 18 days to build one nest

Answer 2

It has to be remembered that, $\quad$

"If 18 birds can make 18 nests in 18 days, then one bird WON'T TAKE ONLY ONE DAY to make one nest!"

Most ones have had such an answer psychologically due to symmetry in the question, but the reason for it being wrong is given below.

Usually the question assumes that the 18 birds are making 18 nests simultaneously in 18 days, and each bird has the same efficiency and power to make one nest.

We know that,

p : The quantity of a job to be done is directly proportional to the time taken for doing that job, if the no. of workers remains unchanged.

Lesser the amount of job to be done, shorter is the time required, for a constant no. of workers.

Thus, the given assumption is logically true that,

★ 18 birds take 18 days to make 18 nests.

★ 18 birds take 1 day to make 1 nest.

And it is also known that,

q : As the no. of workers for doing a particular (constant amount of) job decreases, the time taken for completing that particular job of the same amount increases, i.e., both are inversely proportional.

Hence the given assumption is also logically true, that,

★ 18 birds take 1 day to make 1 nest.

★ 1 bird takes 18 days to make 1 nest.

Hence 18 days is the actual answer.

Now, if one says that "it is true that one bird can make one nest in one day," the statement will be possible and true if and only if 18 birds can make 324 nests in 18 days instead of 18 nests!!!

[For the two concepts p and q, consider the use of proportionality in the questions like "If x people can do a piece of job in m days and y people left the job after n days, then after how many days the remaining ones can complete the remaining job?"]