Question
Mathematics Question on Geometric Progression
If 18C15 + 2(18C16) + 17C16 + 1 = nC3, then n is equal to
A
(A) 19
B
(B) 20
C
(C) 18
D
(D) 24
Answer
(B) 20
Explanation
Solution
Explanation:
18C15+2(18C16)+17C16+1=nC3⇒18C15+18C16+18C16+17C16+1=nC3⇒18C15+18C16+18C16+17C16+17C17=nC3⇒19C16+18C16+18C17=nC3⇒19C16+19C17=nC3⇒2017=nC3⇒n=20