Q: If the coefficients of x7 and x8 in $ (2 + \frac{x}{3})^n$ are equal, then n is
(A) 56
(B) 55
(C) 45
(D) 15
Sol. $\large n_{C_7} \frac{2^{n-7}}{3^7} = n_{C_8} \frac{2^{n-8}}{3^8} $
⇒ n = 55
Hence (B) is the correct answer.
Science and Education
Q: If the coefficients of x7 and x8 in $ (2 + \frac{x}{3})^n$ are equal, then n is
(A) 56
(B) 55
(C) 45
(D) 15
Sol. $\large n_{C_7} \frac{2^{n-7}}{3^7} = n_{C_8} \frac{2^{n-8}}{3^8} $
⇒ n = 55
Hence (B) is the correct answer.