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MENTAL MATH PART III
SUBTRACTION & THE LAST OF
HWK #1
SUBTRACTION -TRADING
ONE PROBLEM FOR
ANOTHER
If you would like to change A-B to an easier
problem then you should do what to the
numbers to assure that you get the same
answers?
Add or subtract the same number to both.
Make the number you subtract as easy as
possible to work with!
EXAMPLES
• 198-89
=209-100=109
• 1533-367
= 1566-400=1166
• 121-88
=123-90
=133-100=33
One More Example
2021-857
=2024-860
=2064-900
=2164-1000
=1164
Compensating one digit at a time
3091
-867
-----------2 224
7 to 10 is 3
3+1 =4
But the 9 is now an 8.
8-6 is 2
8 to 10 is 2
0+2 is 2
But the 3 is now a 2.
Compensating one digit at a time
89
78
5
0
6
5
6
9
5
6
6
6
------ ------ ------ ------ ------ -----8
1
2
9
9
0
Compensating one digit at a time
67
4
7
10
1
5
2
5
4
3
3
3
3
----- ----- ----- ----- ----- ----- ----2
2
7
8
1
9
Compensating one digit at a time
9
- 1
--- --8
8
2
--6
7
3
--4
65
4
--1
4
5
5
--9
43
6
--7
2
3
7
--5
12
8
--3
1
9
--2
Compensating one digit at a time
01
---
01
1
--9
01
2
--8
01
3
--7
01
4
--6
01
5
--5
01
6
--4
1
0
7
--3
1
0
8
--2
0
9
--1
What are the possibilities for
digits a,b and x?
a
a
a
a
b
b
b
b
b
b
a
a
a
----- ----- ----- ----- ----- ----- ----?
x
x
x
x
x
x
Each letter is a different digit – find them!
A
- X
--- --4
B
C
--1
C
F
--5
D
E
--1
E
G
--0
F
A
--1
G
D
--7
X
Y
--7
Y
B
--1
Z
Z
--0
If you get
stuck just
text me at
7757220658
For a hint!