Question

An insect crawls up 5 cm every second on a 60 cm vertical rod and then falls down 2 cm over the next second. How many seconds will it take to climb the rod? My answer is 40 but my teacher says it is 39 can't understand. Please explain

Answer 1

Step-by-step explanation:

The insect is climbing 3 cms every 2 seconds effectively(because in the 1st second it climbs 5 cms and in the 2nd it falls 3 cms). So in 108 seconds it will climb 54 cms.

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Answer 2

Here , in the above Question, the following information is given -

An insect crawls up 5 cm every second on a 60 cm vertical rod and then falls down 2 cm over the next second.


Here , we can calculate this as follows -


The insect first crawls up by 5 cm .


Then it moves down by 2 cm .


So , net movement by the insect in 1 second -


=> 5 cm - 2 cm


=> 3 cm .


So , this insect moves at the rate of 3 cm per second .


So.

In 19 seconds -


Distance moved by the insect -


=> 3 × 19 cm


=> 57 cm .


Now , Here , comes the interesting part ..


In the 60th second -


It first moves up by 5 cm .


So , total distance covered by the insect -


=> 57 cm + 5 cm


=> 62 cm .


Now , it doesn't move down. . As It has already climbed over the rod .


So , the insect takes a net of 20 seconds to climb the 60 cm vertical rod .


This is the required answer .


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