Two members are selected out of 20 and here order does not matter so the formula is nCr = n!/(n-r)!r!
Here we know that nC2 = 190 so the best way is to plug in answer choices
start with 20
20C2 = 20!/(20-2)!2!
= 20*19*18*17*16.......*1/18*17*16...*1 2*1
=190
SO the answer is A 20
Hope it helps!! Just remember the formula and things will be easy for you.
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