What is the sum of odd numbers from 10 to 81? Here we will show you step-by-step how to calculate the sum of odd numbers from 10 to 81.
Step 1) We start by finding the first (F) and last (L) odd numbers from 10 to 81. It is easy to do that by simply looking at the numbers. The first odd number is 11, and the last odd number is 81.
F = 11
L = 81
Step 2) Next, we calculate the total odd numbers (T) there are from 10 to 81, using a formula. Here is the formula and the math:
T = (L - F + 2) ÷ 2
T = (81 - 11 + 2) ÷ 2
T = 72 ÷ 2
T = 36
Step 3) Finally, we use the information from Step 1 and Step 2, and another formula, to calculate the sum of odd numbers from 10 to 81, like this:
Sum = (T ÷ 2) × (2 × F + (2 × (T - 1))
Sum = (36 ÷ 2) × (2 × 11 + (2 × (36 - 1))
Sum = 18 × (22 + 70)
Sum = 18 × 92
Sum = 1656
Sum of odd numbers from 10 to 81 = 1656
Sum of Odd Numbers Calculator
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