Question

Find n, if the sum of n items of A.P 48, 45, 42, ....... is 408 *

n = 16 or n = 15
n = 15 or n = 17
n = 16 or n = 17
n = 17 or n = 18

Answer 1

Answer:

A.P. is 48,45,42..........

Now,a= 48 and d = 45-48 = –3

sum of n terms = n{2a+(n-1)d}/2

Now, 408 = n{2×48+(n-1)(-3)}/2

408×2 = n{96–3n+3}

816 = n(99–3n)

816 = 99n–3n²

3n²-99n+816 = 0

n²-33n+272 = 0

n²–16n–17n+272 = 0

n(n-16)–17(n-16) = 0

(n–16)(n–17) = 0

So, the value of n = 16 or 17

Answer 2

Answer:

Step-by-step explanation:

SOLUTION