Chapter 2 Our Number System, Addition And Subtraction Examples And Worksheet Page 13
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3045
OUR NUMBER SYSTEM, ADDITION AND SUBTRACTION (CHAPTER 2)
2
Estimate in hundreds the answer to
672
802
432
585
a
b
c
d
¡ 194
¡ 74
¡ 286
¡ 137
3
Estimate in thousands the answer to
3133
1928
595
1799
a
b
c
d
+ 2674
+ 7465
4063
837
+ 3778
2610
+ 3208
4
Estimate using whole thousands, the answer to
3724
4063
1799
2143
a
b
c
d
¡ 1917
¡ 2987
¡ 986
¡ 1367
5
Estimate
a
the amount I will put in my bank account if I have cheques for $176, $239, $318
and $97
2
b
the total distance I travelled in
days if I trav-
589
334
elled
km on Friday and
km on Saturday
the mass to be towed if my horse float weighs 862
c
kg and my two horses weigh 496 kg and 534 kg
d
the difference between the height of Mt Everest
(8848 m above sea level) and New Zealand’s high-
est mountain, Mt Aoraki (3754 m above sea level)
F
ADDING WHOLE NUMBERS
MENTAL ADDITION
Rounding can be put to another use. It can help speed our mental calculations.
To do 9 + 6, we think of 9 as 10 ¡ 1.
And,
Also,
9 + 6
9 + 8
7 + 4
So,
= 10 + 6 ¡ 1
= (10 ¡ 1) + (10 ¡ 2)
= 7 + 3 + 1
= 16 ¡ 1
= 20 ¡ 3
= 10 + 1
= 15
= 17
= 11
EXERCISE 2F
When adding on 9,
first add 10 and
2 + 5 =
3 + 5 =
8 + 6 =
1
Get a friend to time
a
b
c
then take 1.
3 + 4 =
4 + 5 =
4 + 2 =
you as you do these
5 + 7 =
5 + 6 =
8 + 7 =
sets mentally. Just
9 + 8 =
7 + 5 =
2 + 9 =
write down the
4 + 7 =
4 + 9 =
4 + 4 =
answer.
5 + 4 =
9 + 7 =
7 + 0 =
6 + 7 =
7 + 3 =
3 + 8 =
2 + 8 =
7 + 6 =
9 + 6 =
6 + 8 =
2 + 6 =
3 + 9 =
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