This is the kind of question where i faced some difficulty while giving a mock…
the question was similar but what was asked was the amount forward and backward movement of the bird ?????
please explain sir

In this question, we have considered that the bird goes from A to B and back for infinite times, But if we have to find the number of rounds the bird completed or number of times the bird met B, then how can we do that?

Diana, that would be a more painful question. It would be a GP if you notice, and hence we could use the formulae of a GP to solve it. For example if we are told that the bird flies 10 times each way then it would be the first 20 steps and the distance would be 75 (1+1/4+1/16….20 terms) and we could say 75 * [1-(1/4)^20] / [1-1/4].

A better choice would be to check the final answer till infinity (which is 100) and figure out which of the options is very close to 100. If we have gone more than 6 or 8 steps, the answer will be so close to the “infinity” answer as to make no difference (in the above case it will be 99.999xx roughly)

If such a question were to come in the exam, you might choose to attempt it a little later as it involves a little more calculation/effort.

The bird travels 80km in forward and 20 in reverse. Is it correct ?
Taking 1/16 as the ratio for the gp.
Also is there any other method to find the forward and reverse distances?

This is the kind of question where i faced some difficulty while giving a mock…

the question was similar but what was asked was the amount forward and backward movement of the bird ?????

please explain sir

Girish, that is exactly the question I would be discussing tomorrow ðŸ™‚ It is a direct consequence of this one…

regards

J

In this question, we have considered that the bird goes from A to B and back for infinite times, But if we have to find the number of rounds the bird completed or number of times the bird met B, then how can we do that?

Diana, that would be a more painful question. It would be a GP if you notice, and hence we could use the formulae of a GP to solve it. For example if we are told that the bird flies 10 times each way then it would be the first 20 steps and the distance would be 75 (1+1/4+1/16….20 terms) and we could say 75 * [1-(1/4)^20] / [1-1/4].

A better choice would be to check the final answer till infinity (which is 100) and figure out which of the options is very close to 100. If we have gone more than 6 or 8 steps, the answer will be so close to the “infinity” answer as to make no difference (in the above case it will be 99.999xx roughly)

If such a question were to come in the exam, you might choose to attempt it a little later as it involves a little more calculation/effort.

regards

J

What if the bird speed is lesser than that of train. Will this logic work in that case as well?

Er, no….in that case the problem cannot even be formulated as the bird will never meet the other train before the crash.

regards

J

how we got 75 in gp ?

Last line of the para beneath 1st pic?

regards

J

The bird travels 80km in forward and 20 in reverse. Is it correct ?

Taking 1/16 as the ratio for the gp.

Also is there any other method to find the forward and reverse distances?

The next posts might help (see the second question) https://cat100percentile.com/2013/07/16/singles-6/

regards

J