Question

the sum of all two digit odd number is what is the solution​

Answer 1

Step-by-step explanation:

all two digit odd numbers are 11, 13, 15,....,99.

This form an A.P. where first term (a)=11

common difference (d) =2

last term (l) = 99

let nth term be 99.

Then, a+(n-1)d= 99

11+(n-1)*2= 99

(n-1)*2= 88

(n-1)= 44

n= 45

so that sum of all two digit odd numbers

$= \frac{n(a + l)}{2} \\ = \frac{45(11 + 99)}{2} \\ = \frac{45 \times 110}{2} \\ = 45 \times 55 \\ = 2475$