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Question : What is the sum of all two-digit odd numbers?

Option 1: 2375

Option 2: 2475

Option 3: 2325

Option 4: 2425


Team Careers360 23rd Jan, 2024
Answer (1)
Team Careers360 24th Jan, 2024

Correct Answer: 2475


Solution : Use the formulas:
n th term = first term + (n – 1) × common difference
Sum of an arithmetic sequence, S = $\frac{\text{number of terms}}{2}×\text{(first term + last term)}$
Two-digit odd numbers : 11,13,15, ........, 97, 99
Common difference = 2
Number of terms, n $=\frac{(99-11)}{2} + 1 = 44 + 1 = 45$
Sum of an arithmetic sequence, S $=\frac{45}{2}×(11+99) = 22.5 × 110 = 2475$
Hence, the correct answer is 2475.

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