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Mathematics

Average of Two Numbers

Arithmetic mean. Free online Average of Two Numbers. Calculate average of two numbers online — fast, accurate, mobile-friendly, no signup needed.

Average
15

Derivation

  1. ├── 01Givena = 10, b = 20
  2. ├── 02Formula(e.a+e.b) / 2
  3. ├── 03Substitute(e.10+e.20) / 2
  4. └── 04Compute Average15
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§01What is

Understanding the Average of Two Numbers

The Average of Two Numbers computes Average from 2 inputs: a, b. Arithmetic mean.

Mathematics shows up in every corner of daily life — budgeting, cooking, construction, engineering, even reading a bus schedule. A calculator like this lets you skip the scratch-paper step and move straight to the answer, without the arithmetic mistakes that creep in when the numbers get messy. The Average of Two Numbers sits in that toolkit — it arithmetic mean. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

(e.a+e.b) / 2

Where

a
a
b
b
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: a = 10, b = 20.

  1. 01Start by noting the input — a: 10.
  2. 02Start by noting the input — b: 20.
  3. 03Substitute these values into the formula: (e.a+e.b) / 2
  4. 04Compute Average: the calculator returns 15.
  5. 05Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Average of Two Numbers Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

a halved

a = 5 (from 10)

Keep every other input at its default and halve the a. See how average responds.

  1. 01New a: 5
  2. 02Baseline Average: 15
  3. 03New Average: 12.5
  4. 04Average decreases by 16.7% → use this sensitivity to plan for real-world variation.
02 · PATTERN

a doubled

a = 20 (from 10)

Keep every other input at its default and double the a. See how average responds.

  1. 01New a: 20
  2. 02Baseline Average: 15
  3. 03New Average: 20
  4. 04Average increases by 33.3% → use this sensitivity to plan for real-world variation.
03 · PATTERN

b halved

b = 10 (from 20)

Keep every other input at its default and halve the b. See how average responds.

  1. 01New b: 10
  2. 02Baseline Average: 15
  3. 03New Average: 10
  4. 04Average decreases by 33.3% → use this sensitivity to plan for real-world variation.
04 · PATTERN

b doubled

b = 40 (from 20)

Keep every other input at its default and double the b. See how average responds.

  1. 01New b: 40
  2. 02Baseline Average: 15
  3. 03New Average: 25
  4. 04Average increases by 66.7% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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