Question

find the first sum of the odd numbers between 0 and 50

Answer 1

odd numbers=1,3,5,7...........49
sn=n/2[2a+(n-1)d]
49=1+(n-1)2
49=1+2n-2
49=2n-1
50/2=n
n=25
s25=25/2(2(1)+(24)2)
=25/2[2+48]
=25/2[50]
= 25*25
=625
therefore the first sum of the odd numbers between 0&50=625

Answer 2

Solution :

The odd numbers between 0 and 50 are 1, 3, 5, .. , 49. They form an AP and there are 25 terms.

∴ Their sum = $\frac{25}{2} (1 + 49) = \frac{25}{2} \times 50$

                    = 25 × 25 = 625