Nathan works out 23 × 12.4 without a calculator - OCR - GCSE Maths - Question 3 - 2017 - Paper 1
Question 3
Nathan works out 23 × 12.4 without a calculator.
This is Nathan's working.
10 × 12.4 = 12.40
20 × 12.4 = 24.80
3 × 12.4 = 37.2
23 × 12.4 = 24.80 + 37.2 = 62
Nath... show full transcript
Worked Solution & Example Answer:Nathan works out 23 × 12.4 without a calculator - OCR - GCSE Maths - Question 3 - 2017 - Paper 1
Step 1
Explain the error that Nathan has made
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Answer
Nathan has not correctly moved the decimal point when multiplying 12.4 by 10. In his calculations, he treated 12.4 as a whole number rather than adjusting for the decimal. When multiplying by 10, the decimal point should shift one place to the right, so the correct computation should show:
10imes12.4=124
Instead, he wrote it as 12.40.
Step 2
Work out the correct answer
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Answer
The correct calculation can be structured as follows:
Calculate using correct intermediate values:
For 20: 20imes12.4=248
For 3: 3imes12.4=37.2
Add these two results to find the total for 23:
248+37.2=285.2
