--- title: "Calculating the mean" description: "Calculate and interpret the mean as an average of a data set" canonical: https://lightmysky.com/learn/mathematics/calculating-the-mean-mt_Cg8VPguS_V source: https://lightmysky.com/learn/mathematics/calculating-the-mean-mt_Cg8VPguS_V.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Calculating the mean Calculate and interpret the mean as an average of a data set Subject: Mathematics · Area: Data & Statistics · Ages 10 to 11 Page: https://lightmysky.com/learn/mathematics/calculating-the-mean-mt_Cg8VPguS_V ## Ready when they can - Calculate the mean of five test scores: 72, 85, 90, 68, 95 - Explain what the mean represents and how it differs from individual data values - Find a missing data value given the mean and all other values ## Lesson: Calculating the mean The mean is one kind of average. To find it, add up every value in a data set. Then divide that total by how many values there are. **Example.** Five pumpkins go on the market scale: 2 kg, 3 kg, 4 kg, 4 kg, and 5 kg. Add them: 2+3+4+4+5=18. Divide by the 5 pumpkins. 5 goes into 18 three times with 3 left over. Keep going: add a decimal point and a zero, and 30 tenths ÷ 5 = 6 tenths. So 18÷5=3.6, and the mean mass is 3.6 kg. No pumpkin on that scale weighs 3.6 kg. The mean is one fair number for all five together. *(drawing: None of these five kids scored exactly 8, but the mean of the group is 8.)* The mean is the total shared evenly between all the values. It can differ from every value in the set. Multiplying the mean by the count gives the total again. For another group with about the same mean, you can estimate its total by multiplying that mean by the new count. This estimate may differ from the total you find by measuring every value. **Example.** Four rounds of a game have a mean score of 6. Three of the rounds scored 5, 8, and 3. First find the total: 6×4=24. Then subtract the known scores: 24-5-8-3=8. The missing round scored 8. Count every entry when finding a mean. Repeated values each count, and a zero counts too. Divide the total by the number of entries, not by the number of gaps between them or the number of different values. After dividing, multiply the mean by the count to check that you get the total back. To find a missing score, multiply the mean by the number of scores to get the total. Add the known scores, then subtract their sum from the total. The mean can be a decimal: to find 3.5 × 4, use 3 × 4 = 12 and four halves = 2, so the total is 14. **Recap.** Mean equals the total of all values divided by how many values there are. ## Practice 14 questions on this page, each with its working shown. ## Needs first - [Statistical analysis vocabulary](https://lightmysky.com/learn/mathematics/statistical-analysis-vocabulary-mt_fmm-P17Vka) - [Addition and subtraction strategies (age 10+)](https://lightmysky.com/learn/mathematics/addition-and-subtraction-strategies-age-10-mt_JH_6RpNWjr) - [Division with Decimals](https://lightmysky.com/learn/mathematics/division-with-decimals-mt_lU-2aTRB9f) ## Opens up - [Averages from frequency tables](https://lightmysky.com/learn/mathematics/averages-from-frequency-tables-mt_5WF_Rhdb1X) - [Comparing data sets with averages and range](https://lightmysky.com/learn/mathematics/comparing-data-sets-with-averages-and-range-mt_XSXnTQoQ4l)