Question

21+23+25+……………+99= ?
PLEASE answer this ​

Answer 1

From question:

a = 21

d = 2

a(n) = 99

S(n) = ?

We Know That:

$a(n) = a + d(n - 1) \\ 99 = 21 + 2(n - 1) \\ 99 = 21 + 2n - 2 \\ 99 = 19 + 2n \\ 99 - 19 = 2n \\ 80 = 2n \\ 40 = n$

$S(n) = \frac{n}{2} (a + a(n)) \\ S(40) = \frac{40}{2} (21 + 99) \\S(n) = 20(120) \\ S(n) = 2400$

Hope this helps.

Thanks.

Answer 2

Answer:

2400

Step-by-step explanation:

Your answer is:-

21+23+25+……………+99

= 2400

HOPE IT HELPS YOU