If C(28, 2r) = C(28, 2r - 4), then what is r equal to?
If C(28, 2r) = C(28, 2r - 4), then what is r equal to? Correct Answer 8
Concept:
Properties of combination:
nCr = nCn-r
If nCx = nCy then n = x + y
Calculation:
Given:
C(28, 2r) = C(28, 2r - 4)
⇒ 28C2r = 28C2r - 4
As we know, If nCx = nCy then n = x + y
Here n = 28, x = 2r and y = 2r - 4
⇒ 28 = 2r + 2r - 4
⇒ 32 = 4r
∴ r = 8
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Feb 20, 2025