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

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Math Expert
Joined: 02 Sep 2009
Posts: 58428
A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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25 Mar 2019, 01:12
00:00

Difficulty:

65% (hard)

Question Stats:

47% (03:16) correct 53% (02:16) wrong based on 17 sessions

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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 [ 20.26 KiB | Viewed 358 times ]

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Joined: 18 Aug 2017
Posts: 5031
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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Updated on: 25 Mar 2019, 04:48
Bunuel wrote:

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

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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Joined: 07 Oct 2018
Posts: 57
Re: A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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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]
GMAT Club Legend
Joined: 18 Aug 2017
Posts: 5031
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
A number of linked rings, each 1 cm thick, are hanging on a peg. The  [#permalink]

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25 Mar 2019, 04:44
1
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
Shreshtha55
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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