October 21-25
Reminders:
Review: adding and subtracting decimals
Math: We are beginning to explore multiplication strategies. Understanding the pattern can be helpful. Every multiplication has a twin, which may be easier to remember.
For example, if you forget 8×2, you might remember 2×8=16. This way, you only have to remember half the table.
Other tips we discussed:
Math Multiplication: Tricks by Number
2: add the number to itself (in other words, double it)
Example 2×9 = 9+9 = 18
4: double, then double again
Example 4×9: double 9 is 18, double 18 is 36
5: Cut in half, then times 10
Example: 5x6: Cut 6 in half to get 3, then times 10 for 30
Or times 10 then cut in half
Example: 5x9: 9 times 10 is 90, then cut in half for 45
Also the last digit goes 5, 0, 5, 0, ... like this: 5, 10, 15, 20, ...
6: when you multiply 6 by an even number, they both end in the same digit.
Examples: 6×2=12, 6×4=24, 6×6=36, etc
7×8: Think "5,6,7,8": 56=7×8
8: Double, double, double!
Example: 8×6: double 6 is 12, double 12 is 24, double 24 is 48
9: is 10× the number minus the number.
Example: 9×6 = 10×6−6 = 60−6 = 54
the ones digit goes 9, 8, 7, 6, ...: 9, 18, 27, 36, 45, ...
the tens digit goes 0, 1, 2, 3, ...: 9, 18, 27, 36, 45, ...
Subtract one to get the tens digit, and the tens and ones digit together to make 9
Example: 9×5: tens digit is 4, 4 and 5 make 9, so 45
Example: 9×8: tens digit is 7, 7 and 2 make 9, so 72
Fingers Strategy for multiplying by 9
Your hands can help! Example: to multiply 9 by 8, hold your 8th finger down, and count "7" and "2", the answer is 72
10: put a zero after it
Example: 10×2 = 20.
- Retakes are Monday
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- Current Events Oct 30.
Review: adding and subtracting decimals
Math: We are beginning to explore multiplication strategies. Understanding the pattern can be helpful. Every multiplication has a twin, which may be easier to remember.
For example, if you forget 8×2, you might remember 2×8=16. This way, you only have to remember half the table.
Other tips we discussed:
Math Multiplication: Tricks by Number
2: add the number to itself (in other words, double it)
Example 2×9 = 9+9 = 18
4: double, then double again
Example 4×9: double 9 is 18, double 18 is 36
5: Cut in half, then times 10
Example: 5x6: Cut 6 in half to get 3, then times 10 for 30
Or times 10 then cut in half
Example: 5x9: 9 times 10 is 90, then cut in half for 45
Also the last digit goes 5, 0, 5, 0, ... like this: 5, 10, 15, 20, ...
6: when you multiply 6 by an even number, they both end in the same digit.
Examples: 6×2=12, 6×4=24, 6×6=36, etc
7×8: Think "5,6,7,8": 56=7×8
8: Double, double, double!
Example: 8×6: double 6 is 12, double 12 is 24, double 24 is 48
9: is 10× the number minus the number.
Example: 9×6 = 10×6−6 = 60−6 = 54
the ones digit goes 9, 8, 7, 6, ...: 9, 18, 27, 36, 45, ...
the tens digit goes 0, 1, 2, 3, ...: 9, 18, 27, 36, 45, ...
Subtract one to get the tens digit, and the tens and ones digit together to make 9
Example: 9×5: tens digit is 4, 4 and 5 make 9, so 45
Example: 9×8: tens digit is 7, 7 and 2 make 9, so 72
Fingers Strategy for multiplying by 9
Your hands can help! Example: to multiply 9 by 8, hold your 8th finger down, and count "7" and "2", the answer is 72
10: put a zero after it
Example: 10×2 = 20.
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