EDEXCEL GCSE FOUNDATION MATHS - What are Sensible Estimates

Edexcel GCSE Foundation Maths: Sensible Estimates

What are Sensible Estimates?

Sensible estimates are rough calculations used to approximate an answer without performing the exact calculation. They are helpful for:

• Checking the reasonableness of a calculated answer.
• Making quick calculations in real-world situations.
• Understanding the magnitude of a number.

How to Make Sensible Estimates:

1. Round the numbers: Round each number to the nearest 10, 100, or 1000, depending on the problem.
2. Perform the operation: Use the rounded numbers to carry out the calculation (addition, subtraction, multiplication, division).
3. Interpret the estimate: Consider if the estimate is too high or too low compared to the actual answer.

Example:

Question: Estimate the cost of 17 apples if each apple costs £0.85.

Solution:

1. Round: Round 17 to 20 and £0.85 to £1.
2. Calculate: 20 apples * £1/apple = £20.
3. Interpret: The estimate of £20 is likely to be slightly higher than the actual cost because we rounded the number of apples and the price up.

Tips for Making Sensible Estimates:

• Think about the context: Consider the situation and what a reasonable estimate would be.
• Use your knowledge of number relationships: Understand the relationship between numbers (e.g., 100 is twice as large as 50).
• Don't be afraid to make assumptions: Simplify the problem by making reasonable assumptions.

Practice Questions:

1. Estimate the total cost of 32 books if each book costs £7.99.
2. Estimate the sum of 12.45 + 6.82.
3. Estimate the product of 4.3 x 9.7.

Key Points to Remember:

• Sensible estimates are not exact answers, but they provide a useful approximation.
• The accuracy of an estimate depends on the degree of rounding used.
• Practice making estimates in different situations to develop your skills.