Question

A monkey jumps 5 yards every second on a 60 yards vertical pole and then falls down 2 yards over the next second. How many seconds will it take to climb the pole?
A. 12
B. 39
C. 40
D. 30

Answer 1

Hint: Try to find the distance covered by the monkey in one second. Using the given data, we can find the distance covered by the monkey in 2 seconds, which helps in finding the distance covered in one second.

Complete step-by-step answer:
It is given that a monkey jumps 5 yards every second and then falls down 2 yards over the next second.
According to the question, for every 2 seconds, the monkey jumps 5 yards and falls down 2 yards.
That means after every 2 seconds, the monkey just climbs$\left( {5 - 2} \right) = 3$ yards.
Simply, the total height of the tree is 60 yards and the monkey has to climb and reach to the top of the tree.
The monkey can climb 3 yards in 2 seconds. Then we can find the distance covered by the monkey in one second as:
$\dfrac{3}{2} = 1.5$yards per second.
Therefore, the monkey climbs $1.5$ yards in one second.
Therefore to climb 60 yards, time is taken$ = \dfrac{{60}}{{1.5}} = 40$ seconds.
But, this is the wrong solution.
The problem takes place in the last 2 seconds.
For deep understanding, we take the distance when time is 36 seconds.
The distance covered in 36 seconds.
Distance$ = \dfrac{{36}}{{1.5}} = 54$yards.
According to the question:
The monkey climbs 5 yards for one second and falls down 2 yards for the next second.
Therefore,
At 37 second,
The monkey climbs 5 yards and reaches distance $ = 54 + 5 = 59$yards.
At 38 second,
The monkey falls 2 yards and reaches at the distance$ = 59 - 2 = 57$yards.

Similarly in 39 seconds,
The monkey climbs 5 yards and reaches at the distance $ = 37 + 5 = 62$yards.
But the tree is 60 yards. That means he already reached the top of the tree.
That means a monkey can reach 60 yards or top of the tree in 39 seconds.

Therefore the option B is correct.

Note: The monkey is climbing $3$yards every 2 seconds, it gives that the monkey climbs the pole in 39 seconds because at $38$ second, the location of the monkey is $57$yards. Then the next jump $5$ yard of the monkey makes him reached the top, so no need to gets down on the next second.