Question

1+2+3+......24+25+24.....3+2+1​

Answer 1

Answer:

625

Step-by-step explanation:

$1 + 2 + 3 + .........24 + 25$

S =

$\frac{n}{2} (a + l)$

n = number of terms of AP = 25 , a = first term of AP = 1 , l = last term of AP = 25

S =

$\frac{25}{2}(1 + 25) \\ \frac{25}{2} (26) \\ 25 \times 13 \\ 325$

$24 + 23 + ..... + 2 + 1$

a = first term of AP = 24 , l = last term of AP = 1 , n = number of terms of AP = 24

s =

$\frac{24}{2} (24 + 1) \\ 12 \times 25 \\ 300$

.: s + S = 300 + 325

625

Answer 2

Answer:

a=1,an=25,d=1,n=25

sn =n÷2(a+an)

sn=25÷2×(1+25)

sn=25÷2×26

sn=25×13

sn=325

similarly other term is also 325

so

325+325=650ans