Mathematics for IGCSE & O level - Using A Calculator (Section 2 - No. 3)
What are the 3 options to help check the answer?
Use some method of estimating.
Make sure you've followed the order of operations.
Use a completely different method to calculate the same answer.
Make sure the calculator is working correctly.
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Estimating the answer and following the correct order of operations, will help to ensure the correct answer.