Question

try question no 24 fast answer it in small and understanding in 4 marks.

Answer 1

$a = 20 \\ d = - 1 \\ sn = 200 \\ \frac{n}{2} (2 \times 20 - n + 1) = 200 \\ {n}^{2} - 41n + 400 = 0 \\ (n - 25)(n - 16) = 0 \\ n = 25 \: or \: 16 \\ if \: n = 16 \\ an = 20 + 15 \times - 1 = 20 - 15 = 5 \\ if \: n = 25 \\ an = 20 - 24 = - 4 \\ it \: is \: not \: possible \\ so \: \: \\ n = 16 \: \: \\ an = 5$