What is the sum of odd numbers from 20 to 129? Here we will show you step-by-step how to calculate the sum of odd numbers from 20 to 129.
Step 1) We start by finding the first (F) and last (L) odd numbers from 20 to 129. It is easy to do that by simply looking at the numbers. The first odd number is 21, and the last odd number is 129.
F = 21
L = 129
Step 2) Next, we calculate the total odd numbers (T) there are from 20 to 129, using a formula. Here is the formula and the math:
T = (L - F + 2) ÷ 2
T = (129 - 21 + 2) ÷ 2
T = 110 ÷ 2
T = 55
Step 3) Finally, we use the information from Step 1 and Step 2, and another formula, to calculate the sum of odd numbers from 20 to 129, like this:
Sum = (T ÷ 2) × (2 × F + (2 × (T - 1))
Sum = (55 ÷ 2) × (2 × 21 + (2 × (55 - 1))
Sum = 27.5 × (42 + 108)
Sum = 27.5 × 150
Sum = 4125
Sum of odd numbers from 20 to 129 = 4125
Sum of Odd Numbers Calculator
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