MULTIPLICATION AND DIVISION OF DIRECTED NUMBERS
Revision on addition and subtraction of directed numbers
Table of Contents
Note that:
(a). + + = + OR – – = + (Replacing the same signs that apprear together by a positive sign
(b). + – = – OR – + = – (Replacing two different signs that appear together by a negative sign
Example 1: Find the values of the following:
(a). + 7 + (+8) (b) +13 – (+6)
Solution:
(a). + 7 + (+8) = 7 + 8 = 15
(b). + 13 – (+6) = 13 – 6 = 7
Example 2 : Calculate the following (a) 25 – (+3) (b) 12 – (-9)
Solution
(a). 25 – (+3) = 25 – 3 = 22
(b). 12 – (-9) = 12 + 9 = 21
MULTIPLICATION OF DIRECTED NUMBERS
RULES:
- + * – = – OR – * + = – (If different signs are multiplied the answer is NEGATIVE).
- + * + = + OR – * – = + ( If the same signs are multiplied the answer is positive).
Example1: Simplify the following (a) (+12) * (+5) (b) (-3) * (-8)
Solution:
(a). 12 * 5 = 60
(b). -3 * -8 = + 24
Example 2: Find the values of the following (a) -4 * -2 * -2 * -2 * -2 (b) 7 * (-3) * (-1) * (-1) * 20
Solution:
( a). -4 * -2 * -2 * -2 * -2 = – 64 ( rules, we have equal signs to give positive while different sign gives negative)
(b). 7 * (-3) * (-1) * (-1) * 20 = 7*-3 = -21 *-1 * -1 = -21*20 = – 420
DIVISION OF DIRECTED NUMBERS
RULES:
+ ÷ + = + OR – ÷ – = + ( If the sign are divided the answer is positive)
+ ÷ + = – OR – ÷ + = =- (Ie the sign are different theanswer is negative).
Eample 1: work out the following (a) (+80) ÷ (-10) (b) (-25) ÷ (-5)
Solution:
- (+80) ÷ (-10) = – 8 (because the signs are different)
- (-25) ÷ (-5) = + 5(because the signs are the same)
DO THESE:
Simplify the following
(b) (-25) ÷ (-5)
(a). 3 x 5 x 2 x 15 (-9) (b). -8 x (-11) x 9 x (-5)
-5 x 25 x 3 2 x (-33) x (-3)
See also
HIGHEST COMMON FACTOR AND LOWEST COMMON FACTOR
WHOLE NUMBER AND DECIMALS NUMBERS