Multiplication Of Whole Numbers, Decimals, Squares And Square Roots Worksheet With Answers Page 20
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41245 = 250 (to the nearest 10)
Workbook
152 = 200 (to the nearest 100)
4. a) 100; b) 2 200; c) 500; d) 22; e) 80;
f ) 20 000
Repeat this process for multiplication.
5. N 2 500 low estimate; 6. N 450
Lesson focus
Assessment
Have a class discussion about rounding. Why
would we sometimes want to round numbers off?
Pupils should be able to find the estimates of
Ask your class to come up with some practical
sums and products of numbers. Observe the
ideas. Here are some suggestions:
pupils’ responses during lesson. Look at their
•
Sometimes we want to know rough numbers
answers to Exercise 4.
only, and not specifics.
•
When we shop for a few items, and want to
Support activity
keep a running total in our heads, it is much
You may need to drill the pupils on their
easier to round each price off to the nearest
multiplication tables. Revise the expansion
10, for example, and then add the rounded off
method to multiply numbers – a 2-digit number
figure to the running total.
by a single digit number, and so on. Give pupils
the Homework activity for extra practice.
Challenge your class by asking them questions like:
•
“When buying material or paint, we round our
estimate up, not down. Why?” (It is better to
Homework activity
have some material or paint left over, rather
Pupils are to complete questions 4–6 on
than not having enough.)
pages 29 and 30 of the WB.
•
“When we have a fixed amount to spend, and
want to make sure that we have enough money
Lesson 5
Pupil’s Book page 112
to pay for the items we choose, would we round
the individual prices up or down? Why?” (We
Preparation
would rather have money left over than not have
You will need to have:
enough money to pay for our purchases.)
•
Gone over the Quantitative reasoning exercise
Answers
and understand the pattern used.
Lesson focus
Exercise 4
1. a) 1 + 5 = 6; 0.8 + 4.9 = 5.7; Difference: 0.3
This and the next lesson gauges the extent to which
b) 160 + 40 = 200; 163 + 41 = 204;
individual pupils have achieved the objectives
Difference: 4
stated at the beginning of this unit.
c) 110 + 160 = 270; 111 + 159 = 270;
Guide the pupils through the example for Exercise 5.
Difference: 0
Help them to see the pattern and allow them to
d) 8 + 10 = 18; 7.9 + 9.8 = 17.7; Difference = 0.3
complete questions 1–6 on their own.
e) 20 × 10 = 200; 18 × 13 = 234; Difference: 34
f ) 650 × 50 = 32 500; 645 × 45 = 29 025;
If you have time at the end of the lesson, you could
Difference: 3 475
discuss some or all of the questions.
2. a) Patrick: 16, Bunmi: 12
b) 15.6 + 11.9 = 27.5, 28 years (to the nearest
Answers
whole number)
3. a) 35 + 39 = 74 m; b) 39 – 35 = 4 m
Exercise 5
1. 70; 2. 890 or 900; 3. 9; 4. 30; 5. 12; 6. 9
75
Unit 17: Estimation
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