Transcript 1-4 Multiply and Divide Real Numbers

Multiply and Divide
Real Numbers
Honors Math – Grade 8
Get ready for the Lesson
A diver descended into the ocean at a rate of 2.1 meters per minute
over a 3-minute period. What signed number represents the diver’s
final depth at the end of the 3 minutes?
What operation?
Multiplication
KEY CONCEPT
3 2.1
Remember that multiplication is a shortcut
for repeated addition.
Multiplying Signed Numbers
1. If the factors have like signs, the product is
positive!
2. If the factors have unlike signs, the product is
negative!
3 2.1 
6.3
Think…
What is the sign of the sum
of -2.1 + (-2.1) + (-2.1)?
1
 2 
  1   2 
4
 3 
Multiply the absolute
value of the numbers.
Simplify the absolute
values.
Rename the mixed
numbers as improper
fractions.
Cancel where
possible.
Multiply and rename.
The factors have like
signs. The product is
positive!
2 1
1 2
3
4
2
1
1   2
3
4
 5  1 
   1 
 8  4 
Multiply the absolute
value of the numbers.
Simplify the absolute
values.
Rename the mixed
numbers as improper
fractions.
Cancel if possible.
Multiply and rename.
The factors have
unlike signs. The
product is negative!
5 1
1
8 4
5
1
 1
8
4
0.9 4.82
Multiply the absolute
value of the numbers.
Simplify the absolute
values.
4.82
 0 .9
Remember to align the
digits when multiplying
decimals!
Determine the number
of decimal places in
the product.
The factors have
unlike signs. The
product is negative!
Place the decimal
point in the product.
0.9   4.82
KEY CONCEPT
Dividing Signed Numbers
1. If the dividend and divisor have like signs, the product is positive!
2. If the dividend and divisor have unlike signs, the product is negative!
Remember a fraction bar is a division symbol.
 0.0141
 4.7
Divide the absolute
value of the numbers.
Move the decimal point in the
divisor and the dividend.
 0.0141   4.7
Divide.
Simplify the absolute
values.
The dividend and the divisor have like signs. The
quotient is positive!
2.2  (0.055)
Divide the absolute
value of the numbers.
2.2   0.055
Simplify the absolute
values.
Move the decimal
point in the divisor and
the dividend.
Divide.
The dividend and the divisor have unlike signs. The
quotient is negative!
3  3 
3  
5  20 
Divide the absolute
value of the numbers.
Simplify the absolute
values.
Change any mixed
numbers to improper
fractions.
Remember, when dividing
fractions, you must multiply by
the reciprocal of the divisor!
3 3
3 
5 20
Cancel and
multiply.
The dividend and the divisor have like signs. The
quotient is positive!
3
3
3  
5
20