What is the sum of odd numbers from 20 to 100? Here we will show you step-by-step how to calculate the sum of odd numbers from 20 to 100.
Step 1) We start by finding the first (F) and last (L) odd numbers from 20 to 100. It is easy to do that by simply looking at the numbers. The first odd number is 21, and the last odd number is 99.
F = 21
L = 99
Step 2) Next, we calculate the total odd numbers (T) there are from 20 to 100, using a formula. Here is the formula and the math:
T = (L - F + 2) ÷ 2
T = (99 - 21 + 2) ÷ 2
T = 80 ÷ 2
T = 40
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 100, like this:
Sum = (T ÷ 2) × (2 × F + (2 × (T - 1))
Sum = (40 ÷ 2) × (2 × 21 + (2 × (40 - 1))
Sum = 20 × (42 + 78)
Sum = 20 × 120
Sum = 2400
Sum of odd numbers from 20 to 100 = 2400
Sum of Odd Numbers Calculator
Please use the tool below to calculate the sum of odd numbers for another set of numbers.