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A number of linked rings, each 1 cm thick, are hanging on a peg. The

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A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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New post 25 Mar 2019, 01:12
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A number of linked rings, each 1 cm thick, are hanging on a peg. The top ring has an outside diameter of 20 cm. The outside diameter of each of the outer rings is 1 cm less than that of the ring above it. The bottom ring has an outside diameter of 3 cm. What is the distance, in cm, from the top of the top ring to the bottom of the bottom ring?

(A) 171
(B) 173
(C) 182
(D) 188
(E) 210


Attachment:
75b3e762b96f49323740d90a83fdb1339789180e.png
75b3e762b96f49323740d90a83fdb1339789180e.png [ 20.26 KiB | Viewed 274 times ]

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A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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New post Updated on: 25 Mar 2019, 04:48
Bunuel wrote:
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A number of linked rings, each 1 cm thick, are hanging on a peg. The top ring has an outside diameter of 20 cm. The outside diameter of each of the outer rings is 1 cm less than that of the ring above it. The bottom ring has an outside diameter of 3 cm. What is the distance, in cm, from the top of the top ring to the bottom of the bottom ring?

(A) 171
(B) 173
(C) 182
(D) 188
(E) 210


Attachment:
75b3e762b96f49323740d90a83fdb1339789180e.png


from the given info it can be understood that the OD of 1st ring = 20 and ID = 19
total no of rings ; 20-3+1 = 18 rings
the sum of the length of the rings ; 18+19/2 = 171
also the top of the ring is 1 cm and bottom of ring OD is 1 cm so 171+2 = 173 cm
IMO B
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Originally posted by Archit3110 on 25 Mar 2019, 03:21.
Last edited by Archit3110 on 25 Mar 2019, 04:48, edited 1 time in total.
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Re: A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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New post 25 Mar 2019, 04:16
Can someone explain why am I getting different ans using formula n(a+L)/2[sum of n numbers, where n=18,a=3 and l=20]
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A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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New post 25 Mar 2019, 04:44
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Shreshtha55 wrote:
Can someone explain why am I getting different ans using formula n(a+L)/2[sum of n numbers, where n=18,a=3 and l=20]


sum of n nos in consective series is n * (n+1)/2
n= 18 ; so 18* 19 /2 = 171
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A number of linked rings, each 1 cm thick, are hanging on a peg. The   [#permalink] 25 Mar 2019, 04:44
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A number of linked rings, each 1 cm thick, are hanging on a peg. The

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