f the coefficient of the 5th term be the numerically the greatest coefficient in the expansion of (1−x)n, then the positive integral value of n, is

We know that the coefficient of the middle term is the numerically greatest coefficient in the expansion of (1−x)nor (  1+x  )n and its value is   nCn/2 or, nCn+12= nCn−12according as n is even or odd. It is given that the coefficient of the 5th term is the greatest. Therefore, 5th term is the middle term. Thus, there are 9 terms.Hence n = 8.