17. Make a Friendly Number:
A friendly number is a
number that ends with a
“0”.
Numbers with a “0” in the
ones spot are easier to
add with
18. Make a Friendly Number:
For example,
to make 28 a friendly number,
I can add 2 to it
to make it 30
19. Make a Friendly Number:
More examples:
• Add 5 to 35, to make 40
• Subtract 2 from 22 to make 20
20. Make a Friendly Number:
This is how it helps:
9 + 4=
If I make 9 into a 10,
10 + 3=
it is easier to solve
because I’m working with a
friendly number.
21. Make a Friendly Number:
BUT….
Notice how I changed the equation to
10 + 3, NOT 10 + 4
I had to manipulate the equation.
Otherwise, I’m just make a new and different
equation that won’t give the same answer
22. Make a Friendly Number:
In adding, it is called “give and take”.
If you give to one side, you have to
take from the other side.
9 + 4= 13
(give 1) +1 -1 (take 1)
10 + 3= 13 New equation
23. Make a Friendly Number:
In subtracting, it is called
“give/give” or “take/take”.
If you give to one side, you have to
give to the other side.
If you take from one side, you have
to take from the other side.
24. Make a Friendly Number:
Some examples of “give/give” and
“take/take”:
9 – 4= 5
(give 1) +1 +1 (give 1)
10 – 5= 5 New equation
11 – 4= 7
(take 1) -1 -1 (take 1)
10 – 3= 7 New equation
25. Make a Friendly Number:
When you:
• “give & take” adding
• “give/give” subtracting
• “take/take” subtracting
You are compensating!
26. Front-End Adding
When you front-end add you
use expanded notation or
your place values.
27. Front-End Adding
Expanded Notation is breaking your
number into ones, tens and hundreds
Eg. 58 42
5 tens, 8 ones 4 tens, 2 ones
50 + 8 40 + 2
28. Front-End Adding
• Front-end adding is when you start adding
from the left and move to the right
Eg. 34 + 45
- start with the tens: 30 + 40 = 70
- now the ones: 4 + 5 = 9
Now you`re working with a friendly number
70 + 9 = 79
29. Let’s Review the Mental Math
Strategies
• Count on
• Doubles
• Near Doubles
• Make a Friendly Number
• Front-End Adding or
Expanded Notation