What is the sum of all two digit odd numbers?

This question was previously asked in
SSC CHSL Tier-I Exam 2022 Official Paper (Held On: 17 March, 2023 Shift 1)
View all SSC CHSL Papers >
  1. 2375
  2. 2475
  3. 2325
  4. 2425

Answer (Detailed Solution Below)

Option 2 : 2475
Free
SSC CHSL Exam 2023 Tier-I Official Paper (Held On: 02 Aug 2023 Shift 1)
2.6 Lakh Users
100 Questions 200 Marks 60 Mins

Detailed Solution

Download Solution PDF

Concept Used:

The sum (S) of an arithmetic sequence can be calculated using the formula:

S = n/2 × (a + l)

where:

S is the sum of the sequence,

n is the number of terms,

a is the first term, and

l is the last term.

The number of terms (n) in an arithmetic sequence can be found using the formula:

n = (last term - first term)/difference + 1

Calculation:

Two-digit odd numbers range from 11 to 99. Since they are odd, they increase by a difference of 2 each time, forming an arithmetic sequence.

Number of terms (n):

n = (99 - 11)/2 + 1 = 44 + 1 = 45

Sum of an arithmetic sequence:

S = 45/2 ×  (11 + 99) = 22.5 ×  110 = 2475

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

Option 2 is the correct answer.

Latest SSC CHSL Updates

Last updated on May 28, 2025

-> The SSC has released the SSC CHSL exam calendar for various exams including CHSL 2025 Recruitment. As per the calendar, SSC CHSL Application process will be active from 23rd June 2025 to 18th July 2025. 

-> The Exam Date for the SSC CHSL 2025 will be from 8th September 2025 to 18th September, 2025. 

-> The SSC CHSL is conducted to recruit candidates for various posts such as Postal Assistant, Lower Divisional Clerks, Court Clerk, Sorting Assistants, Data Entry Operators, etc. under the Central Government. 

-> The SSC CHSL Selection Process consists of a Computer Based Exam (Tier I & Tier II).

-> To enhance your preparation for the exam, practice important questions from SSC CHSL Previous Year Papers. Also, attempt SSC CHSL Mock Test.  

Get Free Access Now
Hot Links: teen patti bodhi teen patti bliss teen patti diya