5. The sum of all two digit odd numbers is.
(a) 2575
(b) 2475
(c) 2524
(d) 2425

Dear Student

The number will start from 11 and end with 99

and common difference d=2 so the numbers are in AP

Tn = 99 , a = 11 , d=2

Tn = a + (n - 1)d

⇒99 = 11 + (n - 1)2

⇒99-11 = (n - 1)2

⇒88 = 2(n - 1)

⇒44 = n-1

⇒n = 45

Now sum of terms,

sum = n(a + l)/2 where l = 99

sum = 45(11 + 99)/2

  = 45 × 110/2

 = 45×55

 = 2475, so the sum of digits are 2475
option-B is correct

Regards