Page 7 - Mathematics-for-the-Senior-Phase-Grades-7-9_Neat
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Senior Phase Mathematics: Grade 7 – 9 Learner book
A method for multiplying
Worked example: Calculate 13 × 54
13 × 54 = 13(50 + 4) so we can calculate 13 × 50 and 13 × 4 and then add them.
Put the numbers under each other in the tens and units columns.
2 1 3 1
4
To calculate à«šà«œ ൈ à«žà«™ 1 2 To calculate à«šà«œ ൈ à«
0 → 3 ൈ 4 ൌ 12
→ put 0 in the units 1 2
column and then just ൈ5 So put 2 in the units column
multiply by 5 and carry 1 to the tens column
5
→ 5 ൈ 3 ൌ 15 so put 5 in 65 → 1 ൈ 4 ൌ 4 and ൅1 ൌ 5
the tens column and 70
carry 1
3
→ 5 ൈ 1 ൌ 5 and ൅1 ൌ 6
Add 52 + 650
Division We can think of division in two ways.
A. Division as making groups: B. Division as equal sharing:
Share 12 sweets equally between 3 friends.
How many sweets will each friend get?
12 sweets. Put them into packets with Grade 7, 8 and 9
3 in each packet. How many packets?
12 ൊ 3
12 ൊ 3
A method for dividing
Worked example: Calculate 192 ൊ 3. We want to know how many 3s there are in 192.
1 64 2
3 1 9 12
There are no 3s in 1 but Add the remainder of 1 ten to
there are six 3s in 19 the units column to get 12.
with 1 ten remainder. 3
64 There are four 3’s in 12
Answer: 3 1 9 2 with no remainder.
Approximation
It is useful to estimate the answer to a calculation before doing the calculation. It is so easy
to make a mistake in a calculation, even when you use a calculator! If your calculated
answer is wrong, you will see that it is not close to your estimate.
Worked examples:
1. Estimate the answer to 48 × 103.
Round off 48 to 50 and 103 to 100.
50 × 100 = 5 000. So 48 × 103 ൎ 5 000.
If you calculate 48 × 103, the answer should be close to 5 000.
2. Approximate the answer to 25 116 ÷ 483.
25 116 ൊ 483 ൎ 25 000 ൊ 500 ൌ 50. So we expect a calculated answer close to 50.
Winning Teams & OLICO 4
