Question

find the sum of all 2 digit odd positive number?

Answer 1

Hi frnd here is ur ans,


Two digit odd positive numbers are 11,13,15,17...........99 are in A.P.
Here a = 11 and d = 2, tn= 99, n = ?

Sum of the n terms = (n/2)[2a+(n -1)d]
But tn = a + (n -1)d
⇒ 99 = 11+ (n-1)2
⇒ 99 -11 = (n-1)2
⇒ 88/2 = (n-1)
∴ n = 45.

subsitute n = 45 in sum of the n terms we obtain

⇒ s45 = (45/2)(2×11 + (45 -1)2)
⇒ s45 = (45/2)(110)
⇒ s45 = 45×55.
⇒ s45 = 2475.

∴sum of all two digit odd positive numbers = 2475.

...i hope this will help you pls mark as brainliest ☺

Answer 2

Answer:2475

Step-by-step explanation:

11,13,15,17..........99

a=11

d=13-11

=2

l =99

n=?

l=a+(n-1)d

99=11+(n-1)2

99=11+2n-2

99=9+2n

99-9=2n

90=2n

n=90/2

n=45

Sn=n/2(a+l)

S45=45/2(11+99)

S45=45/2(110)

S45=45×55

S45=2475

Therefore, sum of all two digit odd positive number are 2475