Latest Elitmus Aptitude Question SOLUTION: A basket ball is dropped from a height of 20 feet. It bounces back each time to a height which is one half of the height of last bounce.How far approximately will the ball have tra

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(#M40018477) ELITMUS question Heights and Distances Keep an EYE

A basket ball is dropped from a height of 20 feet. It bounces back each time to a height which is one half of the height of last bounce.How far approximately will the ball have travelled before it comes to rest
A)30 feet
B)40 feet
C)60 feet
D)Can not be determined

Asked In Elitmus Sumit Rawal (11 years ago)

Unsolved Read Solution (13)

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ranjeet singh chauhan  (10 years ago)

There is a shortcut for these type of question to save time.

suppose it is given it jumps 4/5 to its height, then simply do(4+5)* height.

In this question it jumps 1/2 its height, then (1+2)*20= 60 answer

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zen mano  (11 years ago)

approximate of 60 feet

(1*20)+(2*10)+(2*5)+(2*2.5)+(2*1.25)+(2*.625)+(2*.3125)= 60 feet

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babu rao ganpat rao apte  (10 years ago)

my answer is correct,,saw it in arun sharma....
its 60...

two gp will be there---20(1/1-.5)+ 20(1/1-.5) ...coz when ball bounces it covers twice the distance...the answer will come...80....now substract 20 frm it..coz in first step we are dropping the ball from a height..it is not bouncing at first case

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Nani  (10 years ago)

it is dropped from a height of 20 feets, then it bounces back each time to a height which is one half of the last bounces. so,10 for going up and 10 for coming back, again 5 for going up and 5 for coming down.
now, sum of infinity = a/(1-r)= 10/(1-1/2), here r=t2/t1=5/10=1/2.
so sum of infinity=20. so coming is 20 then going up is also 20. 20+20=40 and the first is 20, so the total is 20+40=60.
so, the correct answer is 60.

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Krishanu chatterjee  (10 years ago)

to me it is 60

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Pratyush  (10 years ago)

20+[20/(1-1/2)]
=20+40
=60

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DIKSHA RANGNANI  (11 years ago)

a/1-r=40
infinite times

Is this solution Helpfull? Yes (1) | No (9)  

Sumit Rawal  (11 years ago)

Hey diksha r u sure that the answer of these kind of questions is always infinity????

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Jitha Mitra Harivanam  (10 years ago)

The sum S of such an infinite geometric series is:

S = a1 (1/1 - x)
=20(1/(1-0.5))
=40 feet

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Nani  (10 years ago)

the series is like this 20,10,10,5,5..... because i did not mention the series above

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pooja  (10 years ago)

ans is
60

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shweta sharma  (10 years ago)

wht is d rght answer?

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Priyansh   (10 years ago)

its a simple gp progression of infinite terms ,,,, frst the ball goes 20 ft down thus travelling 20 ft ,, now it follows a gp ,,, as again the ball rises to (20*(1/2)) 10 ft i.e. half of the original,,,20 ft above and again 10 ft down ,,, now it bounces back upto the height of 5 ft and goes 5 ,,, the progression is as 10,5,2.5......................... and so on upto infinity,,, with the common ratio 1/2 now sum of infinite terms is [a/(1-r)] here a=10 r=1/2 Sn= 20 now eact tym ball travels the double distance as it bounces back it also fall to ground thus travelling same distance ,,,,,, hence total in this it travells 20*2=40 and initially it dropped from 20 ft,, thus it also travells 20 ft therefore total a 40+20=60 ft it travells before coming to rest

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