JSS1 Second Term Mathematics Lesson Note – Approximation

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WEEK 2

CONTENTS: APPROXIMATION

• Rounding off (Rounding up and Rounding down)
• Approximating the results of addition and subtraction
• Approximating the result of multiplication and division.

ROUNDING OFF NUMBERS

Sometimes, when we perform a mathematical calculation, the result may give rise to many more digits than is required. We may approximate the result by giving it a smaller number of significant figures or decimal places. This is called Rounding off. Rounding off numbers may involve rounding up or rounding down. The last digit to be ignored is usually the clue to rounding up or rounding down of the last digit that is kept. If the last digit to be be ignored is 5 or more, the last digit to kept is increased by 1; if it is less than 5, it remains unchanged. In doing this however, the number that is being rounded off must be close to the original as possible.

Examples:

• Round off the following to i) 2 significant figures ii) 3 significant figures
• (a) 9562774 (b) 768.45  (c) 29042

• Round off :

(a) 16540 to nearest thousand b) 48057 to nearest hundred   c) 0.965 to nearest tenth

Solutions:

• To 2 significant figures

768. 9562774 = 9600000 to 2 s.f ii) 768.48 = 770.00 to 2 s.f
769. 29042 = 29000

• a) 16540 = 16600 to nearest thousand b) 48057 = 48100 to nearest hundred

1. 965 = 1.000 to nearest tenth

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