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25 Dec 2025

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Estimating Calculations Made Easy

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@sklwork

Estimating helps you quickly work out approximate answers to complex... Show more

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Estimating Calculations

When estimating calculations, follow three simple steps: round each number to a suitable accuracy, work out the answer using these rounded numbers, and show all your workings. This approach gives you a quick ballpark figure to check against your final answer.

Let's look at how this works with some examples. For calculating 42.6 × 12.1, you would round to the nearest 10: 42.6 ≈ 40 and 12.1 ≈ 10. This gives you an estimated answer of 400, which is much easier to calculate mentally than the original numbers.

With more complex calculations like $\frac{\sqrt{6242-57}}{9.8-47}$ , you can simplify by rounding and handling the square root. First, round to get $\frac{\sqrt{6000-60}}{10-5}$ , which simplifies to $\frac{\sqrt{5940}}{5}$ . Since $\sqrt{5940} \approx \sqrt{10000} = 100$ , your estimated answer is $\frac{100}{5} = 2$ .

Top Tip: When estimating, you can often ignore smaller values in addition or subtraction if they don't significantly affect the final answer. This makes your mental math even quicker!

Real-world problems also benefit from estimation. In the cake business example, estimating how many cakes Jo made from her flour purchases (£984.69) becomes simpler. Round £984.69 to £1000 and £1.89 to £2, giving approximately 500 bags of flour. With 5 cakes per bag, she made about 2,500 cakes last year.

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25 Dec 2025

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1 page

Estimating Calculations Made Easy

👤

@sklwork

Estimating helps you quickly work out approximate answers to complex calculations. By rounding numbers to make them easier to work with, you can check if your final answer is reasonable. This skill saves time and helps catch errors in your... Show more

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Estimating Calculations

Top Tip: When estimating, you can often ignore smaller values in addition or subtraction if they don't significantly affect the final answer. This makes your mental math even quicker!