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The number of connections C that can be made through a switc

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The number of connections C that can be made through a switc [#permalink] New post 31 Jul 2019, 02:31
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100% (00:36) correct 0% (00:00) wrong based on 3 sessions
The number of connections C that can be made through a switchboard to which T telephones are connected is given by the formula \(C=\frac{T(T-1)}{2}\) . How many more connectIOns are possible with 30 telephones than with 20 telephones?

(A) 435

(B) 245

(C) 190

(D) 45

(E) 10
[Reveal] Spoiler: OA

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Re: The number of connections C that can be made through a switc [#permalink] New post 06 Aug 2019, 09:28
Solve for C with T = 20
we get,

C = 20(19)/2
or, C = 10*19 = 190

Again solve for C but this time with T = 30
C = 30(29)/2
or, C = 15(29)
or, C = 435
The difference is 435 - 190 = 245
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Re: The number of connections C that can be made through a switc   [#permalink] 06 Aug 2019, 09:28
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