## Wednesday, October 26, 2011

### Derec's Math Post

1. Put the numbers in a vertical column, aligning the decimal point.
2. Add each column of digits, starting on the right and working and working left . If the sum of a column is more than ten, "carry" digits to the next column on the left.
3. Place the decimal point in the answer directly below the decimal points in the terms.n

(+) + (+) = +
(-) + (+) = -
(+) + (-) = Absolute Value
(-) + (+) = which ever is greater, keep the sign

Subtracting Decimal .
1. Put the numbers in a vertical column, aligning the decimal points.
2. Subtract each column, starting on the right and working left. If the digit being subtracted in a column is larger than the digit above it, "borrow" a digit from the next column to the left.
3. Place the decimal point in the answer directly below the decimal points in the terms.
4. Check your answer by adding the result to the number subtracted. The sum should equal the first number.

(+) - (-) = +
(-) - (+) = -
(+) -(+) = Absolute Value
(-) - (-) = Absolute value

For example.

89.9 + 43.3 = 133.2
1 1
89.9
+ 43.3
_______
133 .2

46.65 - 16.2 = 30.45

46.65
- 16.20
________
30.45

Multiplying and Dividing Decimal

Here are the rules for multiplying decimal numbers:

1. Multiply the numbers just as if they were whole numbers:
*Line up the numbers on the right--do not align the decimal points.
*Starting on the right, multiply each digit in the top number by each digit in the bottom number, just as with whole numbers.
2.Place the decimal point in the answer by starting at the right and moving the point the number of places equal to the sum of the decimal places in both numbers multiplied.

(-) x (+) = -
(+) x (-) = -
(+) x (+) = +
(-) x (-) = +

for example

37.7 x 2.8 =

37.7 ( 1 decimal place )
x 2.8 ( 1 decimal place )
________
3016
+ 754
________
105.56 ( 2 decimal places, move point 2 places left )

To divide decimal numbers:

1. If the divisor is not a whole number, move decimal point to right to make it a whole number and move decimal point in dividend the same number of places.
2. Divide as usual. Keep dividing until the answer terminates or repeats.
3. Put decimal point directly above decimal point in the dividend.

-/- = +
+/+ = +
-/+ = -
+/- = -

for example:

16.9 ÷ 6.5 = 2.6

2.6
____
6.5 /169.0
- 130
__________
390
- 390
__________
0

To check our answer, we multiply the quotient by the divisor and make sure it equals the dividend:

2.6
x 6.5
______
130
+ 156
______
16.90

Homework!
-Finish all worksheets
-Homework Book
-Math Textbook;leftover work