Question

Find sum of all odd number from 351 to 491

Answer 1

Here,
a = 351
an = 491 = l
d = 2(Odd no.s are alternate numbers)
$an = a + (n - 1)d \\ = > 491 = 351 + 2(n - 1) \\ = > 2(n - 1) = 491 - 351 = 140 \\ = > (n - 1) = \frac{140}{2} \\ = > n = 70 + 1 = 71.$


$Sn = \frac{n}{2}(a + l) \\ = > Sn = \frac{71}{2}(351 + 491) \\ = > Sn = \frac{71}{2} \times 852 \\ = > Sn = 71 \times 426 \\ = > Sn = 30246.$


Hope this will help you. 

If you like my answer
Please mark it as brainliest 
And 
Be my follower if possible.