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If ^15Cr: ^15C r – 1 = 11: 5, find r.

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If 15Cr: 15Cr – 1 = 11: 5, find r.

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Best answer

Given as

15Cr: 15Cr – 1 = 11: 5

15Cr / 15Cr – 1 = 11 / 5

Lets use the formula,

nCr = n!/r!(n – r)!

5(16 – r) = 11r

80 – 5r = 11r

80 = 11r + 5r

16r = 80

r = 80/16

= 5

∴ The value of r is 5.

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