What is the sum of odd numbers from 9 to 18? Here we will show you step-by-step how to calculate the sum of odd numbers from 9 to 18.
Step 1) We start by finding the first (F) and last (L) odd numbers from 9 to 18. It is easy to do that by simply looking at the numbers. The first odd number is 9, and the last odd number is 17.
F = 9
L = 17
Step 2) Next, we calculate the total odd numbers (T) there are from 9 to 18, using a formula. Here is the formula and the math:
T = (L - F + 2) ÷ 2
T = (17 - 9 + 2) ÷ 2
T = 10 ÷ 2
T = 5
Step 3) Finally, we use the information from Step 1 and Step 2, and another formula, to calculate the sum of odd numbers from 9 to 18, like this:
Sum = (T ÷ 2) × (2 × F + (2 × (T - 1))
Sum = (5 ÷ 2) × (2 × 9 + (2 × (5 - 1))
Sum = 2.5 × (18 + 8)
Sum = 2.5 × 26
Sum = 65
Sum of odd numbers from 9 to 18 = 65
Sum of Odd Numbers Calculator
Please use the tool below to calculate the sum of odd numbers for another set of numbers.