Behavioural Objectives: At the end of the lesson, the pupils should be able to:

- Write out the rules for estimation to nearest 10
- Write out the estimate of each number given.

RULE 1: FOR 2 – DIGIT NUMBER

- If the unit digit is less than 5, estimate to the lower nearest multiple of 10.
- If the unit digit is greater than 5, estimate to the higher nearest multiple of 10.
- If the unit digit is equal to 5, estimate to the higher nearest multiple of 5.

Example 1.

Write the estimate of the following numbers.

12, 14, 15, 17.

Solution

T u

1 2 > 10 since the expansion of 12 is 10+2 and 2 is the unit which is less than 5.

T u

1 4> 10= 10+4 and 4 is the unit digit which is less than 5.

T u

1 5> 20 since the expansion of 15 is 10+ 5 and 5 is the unit which is equal to 5.

T u

17> 20 since 7 which is 5 .

RULE 2: FOR 3 – DIGIT NUMBER

- If the teens digit is less than 50, estimate to the lower nearest multiple of 100.
- If the teens digit is greater than 50, estimate to the higher nearest multiple of 100.
- If the teens digit is equal to 50, estimate to the higher nearest multiple of 100.

Example 1.

Write out the estimate multiples of 100.

121, 129, 236

Solution

H T U

1 2 1> 100 because 20<50.

H T U

1 2 9> 100 because 20<50.

H T U

2 3 6> 200 Because 30<50

RULE 3: FOR DECIMAL AND VULGAR NUMBER

Note: Vulgar numbers are simple numbers expressed with numerator and denominator. We estimate decimal and vulgar numbers to whole numbers.

RULE 3 FOR DECIMAL AND VULGAR NUMBERS.

- If the decimal or fraction part is less than 0.5 or 1/2, estimate to nearest lower whole number.
- If the decimal or fraction part is greater than 0.5 or 1/2, estimate to the nearest higher whole number.
- If the decimal or fraction is equal to 0.5 or 1/2 estimate to the nearest higher whole number.

Example

Write out the estimate of the following decimal and fraction.

✳️3.2 = 3 because .2<5

3.5= 4 because .5=.5

✳️3¹/5= 3 because 1/5 <1/2 i.e 1/5 is 0.2 while 1/2 is 0.5

3½=4 because 1/2 = ½

ESTIMATION OF 2 DIGIT TO THE NEAREST 10.

Note: In estimation, a number is either rounded up or down to the nearest whole number.

- Numbers less than 5 are rounded down.
- Numbers greater than 5 are rounded up.

Example

Estimate the following 2 – digit number to their nearest 10.

54, 57, 22.

Solution

T u

5 4= 50 because 4 which is unit is not up to 5 .’. you rounded down.

(b). 57= 60 to the nearest tens

(c). 22= 20 because 2 is rounded down.

ESTIMATION OF 3 DIGIT WHOLE NUMBERS TO THE NEAREST 100 AND 4 DIGIT TO THE NEAREST 1000.

Example

Estimate the following 3 – digit to the nearest 100 and 4 digit to the nearest 1000.

(a)458 (b)704 (c) 6500 (d)4437

Solution

458= 500 to the nearest 100

704= 700 rounded down to the nearest 100

6500= 7000 rounded up to the nearest 1000

4437= 4000 rounded down to the nearest 1000.

Exercises.

- Estimate the following 3 – digit to the nearest 109.

(a) 558 (b) 4648 (c) 7500 - Estimate the following 2 digit to their nearest 10.

(a).55 (b). 69 (c). 74

Send your answers to this number 07089083533

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