AQA · Mathematics · 8300
GCSE Maths: Number: estimation
Number · AQA GCSE Maths (8300). Cards are generated from the Corbettmaths textbook exercise and practice questions for Number: estimation (Corbettmaths Video 215), and every card links back to the exact page it came from. Practice tests generate fresh variations of these questions, so the numbers change every attempt. Source material © Corbettmaths — used with attribution.
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What is the first step when estimating the product of two numbers like 39 × 21?
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Round each number to the nearest 10 (or another appropriate place value).
When estimating the cost of 72 packets at 19p each, what rounded calculation would you use?
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Round to 70 × 20p = 1400p = £14.
When estimating a complex expression like (82 × 48) ÷ 198, what is the general approach?
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Round each number to a convenient place value (e.g., nearest 10), then perform the simplified calculation: (80 × 50) ÷ 200 = 4000 ÷ 200 = 20.
When estimating (58.8 × 20.9) ÷ 101.4, how should you round the numbers?
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Round to (60 × 20) ÷ 100 = 1200 ÷ 100 = 12.
When verifying an answer by estimation, what does it mean if your estimate is very different from the claimed answer?
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The claimed answer is likely incorrect. For example, rounding (88.78 − 19.44) ÷ 9.84 to (90 − 20) ÷ 10 = 7 shows an answer of 10.99 is wrong.
When estimating 9.9% of 5987, what simplified calculation could you use?
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Round to 10% of 6000 = 600.
When asked whether an estimate is an overestimate or underestimate, what should you consider?
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Check whether each rounded value was increased or decreased, and how this affects the final calculation.
When estimating how many items can be bought with a given amount of money, what operation should you use?
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Division: divide the total money by the price per item (after rounding to 1 significant figure).
In estimation problems, numbers are typically rounded to ?.
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1 significant figure
When rounding 60.4 to 1 significant figure, what is the result?
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60
When rounding 0.511 to 1 significant figure, what is the result?
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0.5
If you round both numbers in a multiplication up, is the estimate an overestimate or underestimate?
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An overestimate, because you are multiplying larger values than the originals.
What is √20 estimated to the nearest whole number?
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4 or 5 (since √16 = 4 and √25 = 5, and 20 is between them; closer to 4.5 but 4 or 5 are acceptable estimates).
What is √51 estimated to the nearest whole number?
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7 (since √49 = 7 and √64 = 8, and 51 is closer to 49).
What is ³√30 estimated to the nearest whole number?
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3 (since ³√27 = 3 and ³√64 = 4, and 30 is closer to 27).
When estimating a division like 79.7 ÷ 0.0206, what rounding strategy simplifies the calculation?
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Round to 1 significant figure: 80 ÷ 0.02, which equals 4000.
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