Transcript e2e3number - Skills Workshop

Number facts
You need to know your number bonds to 20.
These are all addition facts to 20, and from these you
can learn the subtraction facts.
For example:
7 + 8 = 15 and 15 – 8 = 7
Learn these and then use them to help you with
trickier sums
3 + 9 = 12
9 + 3 = 12
12 – 3 = 9
12 – 9 = 3
Number bonds to 20
Circle 10 pairs of
numbers that total 20.
The pairs of numbers
must be touching,
wither horizontally,
vertically or diagonally.
One has been done for
you.
4
16
3
5
3
6
7
12
10
4
17
7
1
10
0
2
15
13
19
13
16
9
18
1
10
8
6
12
5
15
11
9
14
10
8
2
+
0
1
2
3
4
5
6
7
8
9
10
0
0
1
2
3
4
5
6
7
8
9
10
1
1
2
3
4
5
6
7
8
9
10
11
2
2
3
4
5
6
7
8
9
10
11
12
3
3
4
5
6
7
8
9
10
11
12
13
4
4
5
6
7
8
9
10
11
12
13
14
5
5
6
7
8
9
10
11
12
13
14
15
6
6
7
8
9
10
11
12
13
14
15
16
7
7
8
9
10
11
12
13
14
15
16
17
8
8
9
10
11
12
13
14
15
16
17
18
9
9
10
11
12
13
14
15
16
17
18
19
10
10
11
12
13
14
15
16
17
18
19
20
Rounding
If you need to add or take away 9 or 19, round the
number to 10 or 20 to make it easier
Examples:
16 + 9
37 + 19
34 - 9
63 - 19
Add 10,
Add 20,
Take away 10,
Take away 20,
take away 1
take away 1
add 1
add 1
Answer: 25
Answer: 56
Answer: 25
Answer: 44
You can also use this method to add or take away larger
numbers ending in 9 such as 29, 29 and 49
Adding 2-digit numbers
If you know your number bonds, then adding bigger
numbers in you head is easier.
Example:
35 + 57
Use these three steps:
1. Hold the bigger number in your head: 57
2. Add the tens: 57 + 30 = 87
3. Add the units: 87 = 5 = 92
Complete activity sheets 3.2 and 3.3
Subtracting 2-digit numbers
A really good method for subtraction is to find the
difference between he numbers by counting on.
If it helps, draw
a number line.
Remember to put
the smaller
number on the
left and the
larger number on
the right
Example:
93 – 56 This number line shows
exactly what goes on in your head
56
60
93
Count on from 56 to 60. Hold the 4 in your head.
60 to 93 is 33
33 + 4 is 37
so 93 – 56 = 37
Mental calculations
Calculate the answers and use the code to crack the code:
91 = H
34 + 16 = 50 A
91 – 19 =
45 = S
53 + 19 =
78 – 28 =
50 = A
27 + 23 =
54 – 9 =
16 = R
32 + 9 =
63 – 22 =
72 = M
46 + 45 =
82 – 77 =
41 = T
17 + 28 =
65 – 49 =
5= E
Written addition
If you are given a sum and the numbers are too big, or
there are too many numbers to add in your head, then
you need to use a written method.
3527
Follow this step-by-step method:
1. Write the numbers neatly in a
column, lining up the digits
2. Start by adding from the right-hand
column. For any total over 9 just put
the tens digit under the next column
3. Now do the same with the tens
column. Keep going left until all the
columns have been added.
+768
____
3527
+768
___5
1
3527
+768
4295
1 1
Calculate the answers.
8012
5647
3390
+1579
+3528
+4691
_____
_____
_____
Use the written method to calculate these answers:
37.21 + 16.95
2755 + 346
28.09 + 4.98
When you add decimals, remember to line up the decimal point.
Written subtraction
Here are two good ways to subtract. Have a go at both methods
and choose the one that you feel happier with.
346
- 84
Method 1
1.
Write the numbers in a column, lining up
the units digits
2.
Start from the right-hand column, take
away the bottom number from the top
number.
3.
Now do the same with the other columns.
If the top number is smaller than the
bottom number, then, in this example,
exchange a 100 from the hundreds
column. You are making the 40 into 140
and the 300 into 200
____
346
- 84
2
2 14
346
2146
- 84
- 84
____
262
Method 2
Find the difference between the numbers by counting on.
1. Draw a blank number line
84
2. Count on to the next
ten, then to the next
hundred, then to the
number
6
84
346
10
90
100
3. Add up all the jumps. 246 + 10 + 6 = 262
246
346
Calculate the answers.
7461
9625
5330
- 831
- 2459
-1822
_____
_____
_____
Use the written method to calculate these answers:
63.18 – 45.02 =
4829 – 764 =
13.5 – 9.62 =
When you take away decimals, remember to line up the decimal point.
Try these using any of the above methods:
1. 345 + 267
6. 709 + 426
2. 1485 + 2097
7. 1268 + 691
3. 862 + 28
8. 486 – 127
4. 506 – 329
9. 865 – 426
5. 259 – 102
10. 682 - 327
Word problems
Answer these questions.
1. Meera has saved £27 and has £28 birthday money.
She wants to buy a bike for £72. How much money
does she still need before she can buy the bike?
2. A tourist bus travelled 147km to London, 16km
around the sights of London and then 147km back
home. How far did the bus travel in total?
3. Tom’s Gran is 84 years old. His Mum is 35 years
younger than his Gran and Tom is 38 years younger
than his Mum. How old is Tom?
4. A library needs a bookshelf 2.53 m long and they
have two shelves, 1.48m and 1.7m in length. How
much will have to be cut off one of the shelves to
make them fit?