**Solution:**

We have First odd number is 1

Last odd number is 49

a = 1 an or I = 49 ,common difference d= 2.

a_{n} = a+(n-1)d

=1+(n-1)2 = 49

=1+2n-2 =49

=2n-1 =49

=2n=49+1

=2n=50

n=25

s_{n}=n/2(1+49)

=25/2(1+49)

=25/2* 50

25 *25 = 625

**therefore sum of all odd numbers between 0 to 50 is 625.**