A frog is climbing a greasy pole. The frog can climb 2 centimeters

Question

A frog is climbing a greasy pole. The frog can climb 2 centimeters every half-hour and it takes a break to rest for half an hour after every 2 hours, during which it slips by 1 centimeter. How much time it will take to climb a 28 centimeter pole?

1) 7.5 hours

2) 8.5 hours

3) 9.25 hours

4) 9.75 hours

5) 10 hours

Please provide kudos to help me unlock the GMATclub test.

A) 7.5 hours

B) 8.5 hours

C) 9.25 hours

D) 9.75 hours

E) 10 hours

BrentGMATPrepNow · Accepted Answer

Let's solve this by  making a table

Cheers,
Brent

VenoMfTw · Answer

It will climb 8m in 2hrs ---> then slips 1m in 0.5hr
Thus a total of 7m in 2.5hrs

7m ----> 2.5hr
21m ---> 7.5hr

Remaining 7m it will climb without slipping as distance left(7) is less then the total climb in single attempt(8) 
Thus
8m ----> 2hr
7m ---->?
7*2 = x * 8
x = 1.75

Thus total time = 7.5+1.75 =9.25

GMATinsight · Answer

In such case the caution is to think before the cycle of 2.5 hours end

In every 2.5 hours the Net Movement = 2*4 - 1 = 7 centimeter

i.e. (7*3=)21 cm will be climbed by him in 3*2.5 = 7.5 Hours

Now in 7.5 hours he is at height = 21
in 8 hours he is at height = 21+2 = 23
in 8.5 hours he is at height = 23+2 = 25
  in 9 hours he is at height = 25+2 = 27
and in 9.5 hours he is at height = 27+2 = 29

i.e. He will be at 28 Centimeter height between 9 and 9.5 hour = 9.25 hour

Answer: option C

ENGRTOMBA2018 · Answer

FYI, mentioning the text in red is not cool! Kudos should be given voluntarily by people who think that the post(s) were helpful. You should not be asking for kudos. You can remind them to "thank" you for the post by mentioning what many people do but mentioning it in the way you have done above is not good.

As for the question, in every set of 2.5 hours, the frog's net movement will be 8 = 2*4 - 1 = 7 cm.

Thus in 2.5 * 3 hours, the frog will climb = 7*3 = 21 cm. Now the remaining 28-21 = 7 cm will be done by him in (7/8)*2 = 1.75 hours.

Thus the total time = 7.5+1.75 = 9.25 hours. C is the correct answer.

mvictor · Answer

good one, tried to see the pattern first..
2h = climbs 8 cm
2.5h = 7.
thus, at 7.5h it will be at 21 cm (after the break)
8h=23cm
8.5h=25cm
9h=27cm

since it climbs 2cm every half hour, it means that 1 cm climbs in 0.25h.

thus, 9.25h is needed to climb 28cm

guialain · Answer

Another good question from veritas. It damaged my score since i made a careless mistake.
the frog reaches 28 after 2 rests. no need to add 30 min rest at the end as the frog is already at destination.

pushpitkc · Answer

(1st interval) +2 (2nd interval) +2 (3rd interval) +2 (4th interval) +2 (5th interval) -1(while rest) 
Effectively the frog climbs 7 cm in 2.5 hours. 
Each interval is of half an hour only.

In 7.5 hours, the frog would have climbed 21 cms.
In the next 3 intervals, it would climb 6 cm.
The last cm climb will take it half the time to make the climb of 2 cm(15 mins)
Therefore the total time it takes the frog to climb 28 cm is 9 hours, 15 minutes or 9.25 hours(Option C)

JeffTargetTestPrep · Answer

In 2.5 hours, the frog can climb a total of 8 centimeters but will slip back 1 centimeter; thus, it will have covered a distance of 7 centimeters. We need to be careful not to just conclude that it will take 2.5 x 4 = 10 hours, because once the frog reaches the top, it will not rest and slip back again. Instead, we proceed as follows:

In 7.5 hours, the frog will be 21 centimeters high.

In 8 hours, the frog will be at 23 centimeters.

In 8.5 hours, the frog will be at 25 centimeters.

In 9 hours, the frog will be at 27 centimeters.

Since it takes 0.5 hours to climb 2 centimeters, it will take 0.25 hours to climb the final centimeter, and thus the frog will be on the top of the 28-centimeter pole in 9 + 0.25 = 9.25 hours.

Answer: C

Gemmie · Answer

1. For each 1/2 hour, the frog climbs 2 cm
 
=> For each 1/4 (=0.25) hour, the frog climbs 1 cm
=> For each 2 hours, the frog climbs 8 cm
 
2. After 2 hours, the frog take rest 1/2 hour and slips by 1 cm

=> For 2.5 hours, the frogs climb 7cm

=> Needs less than  2.5 * (\frac{28}{7}) = 10  hours

At after 9.5 hours => the frog already climbs 29 cm (the last 1/2 hour of the 10-hour period is the frog slipping 1cm)
At after 9.25 hours => the frog be climbs 28 cm (since for each 1/4 (=0.25) hour, the frog climbs 1 cm)

=> 9.25 hours

Answer C

A frog is climbing a greasy pole. The frog can climb 2 centimeters

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