GCSE Maths Practice: estimation

Question 1 of 10

Estimate the total of two household bills by rounding each amount to the nearest ten before adding.

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\( \begin{array}{l}\textbf{Estimate: total cost of bills}\\ \text{£324.6+£280.7}\end{array} \)

Choose one option:

Round both values consistently before adding — it helps track spending quickly and accurately.

Estimating Monthly Expenses

In everyday life, we constantly estimate totals — from shopping to budgeting. This question models a real situation: working out the total of two household bills without needing exact precision.

Scenario: Estimating Monthly Bills

Your electricity bill is £324.60 and your internet bill is £280.70. Before paying or planning your budget, you estimate the total: round to the nearest tens — £320 and £280. Add them quickly: 320 + 280 = £600. The real total (£605.30) is very close, confirming that your rounding worked well.

Why Estimate Totals?

Budgeting depends on fast, approximate thinking. When you glance at your bills, you don’t need every penny to know if you’ll stay within budget. Estimation shows whether your total is near £600 or £700 — good enough for planning or double-checking your calculator results.

Step-by-Step Strategy

  1. Round each number to the same place value (usually tens or hundreds).
  2. Add them mentally using known combinations (e.g., 32 + 28 = 60 → 320 + 280 = 600).
  3. Check logic: if both rounded down, the exact total will be slightly higher.

Worked Examples

  • Example 1: £324.6 + £280.7 → £320 + £280 = £600 (actual £605.3).
  • Example 2: £149.3 + £351.8 → £150 + £350 = £500 (actual £501.1).
  • Example 3: £873.2 + £122.9 → £870 + £120 = £990 (actual £996.1).

Understanding Rounding Direction

Rounding both numbers down gives a slightly smaller total; both up gives a slightly larger one. This helps predict whether your estimate will fall below or above the true total. When balancing a budget, it’s safer to round up so you don’t underestimate costs.

Common Mistakes

  • Rounding one number to tens and another to hundreds, which skews the total.
  • Forgetting the units (£) — always include them in written answers.
  • Adding exact and rounded numbers together (e.g., £324.6 + £280 = wrong method).

Real-Life Applications

Estimation like this supports personal finance planning, project management, and even business cost forecasting. Employers value this skill because it shows quick judgment under time pressure.

FAQ

  • Q: How do I decide which place value to round to?
    A: Use tens for everyday money; use hundreds when numbers are large, like annual costs.
  • Q: Should I always round up for bills?
    A: Yes, rounding up avoids surprises when paying the exact amount.
  • Q: Is estimation used in exams?
    A: Yes — exam questions often ask you to ‘estimate’ before calculating precisely to show reasoning.

Study Tip

When estimating with money, imagine paying in round notes (£10s or £100s). It keeps results realistic and makes mental arithmetic intuitive.

Summary

Estimation is a budgeting essential. Rounding £324.60 and £280.70 to £320 and £280 gives £600 — a clear, reliable estimate for quick financial decisions.