Question

The
Sum of all ? digit old
digit old under
11, 13, 15 ,- 99 find n and sn​

Answer 1

Answer:

2475

Step-by-step explanation:

All two-digit odd positive numbers are 11, 13, 15, 17, ...., 99. which are in AP with a=11,d=2,l=99

Let the number of terms be n.

a

n

=99

a+(n−1)d=99

11+(n−1)×2=99

n=45

Sum of n terms is given by

S

n

=

2

n

(a+l)

S

n

=

2

45

(11+99)=2475

Therefore, the sum of all two-digit odd positive numbers is 2475.