Transcript muffin recipe

Dividing Rational
Numbers
Section 2.5
Objectives
• Divide rational numbers.
(NS 1.2)
• Simplify numerical expression
by applying inverse properties
of rational numbers. (AF 1.3)
Words to
Know
• Reciprocal Two numbers whose
product is 1. Also called
the multiplicative inverse.
To divide
fractions…
• Find the reciprocal of the
second fraction.
• Multiply the numerators.
• Multiply the denominators.
• Simplify
Let’s Try
One…
Find the reciprocal
of the second
fraction.
Simplify
Multiply the
numerators.
Multiply the
denominators.
Let’s Try
One…
Make the mixed
number an improper
fraction.
Find the reciprocal of
the second fraction.
Simplify
Multiply the
numerators.
Multiply the
denominators.
Let’s Try
Another…
Find the reciprocal
of the second
fraction.
Simplify
Multiply the
numerators.
Multiply the
denominators.
How do you divide
fractions?
Now You Try…
3
3
4
1

4
4
1
8
1

5
2
15
2 4

3 5
5

6
10 y
3

y
3
10
…A Few More
x
x
 ( 4 ) 
2
8
3b 9b

2
5
5

6
1 4

y y
1

4
10 y
1

n 1
3
4
Dividing
Decimals
Find 0.65 ÷ 0.25
0.25
)0.65
2 .6
25 )65.0
 50
150
–150
0
0.25 has two
decimal places so
multiple both
numbers by 100 to
make the divisor an
integer.
Then divide as a
whole number.
The answer is
reasonable.
Evaluating
Expression
s with
Rational
Numbers
Evaluate the expression for the given value
of the variable.
5.25 for n = 0.15
n
5.25
5.25
=
n
0.15
0.15 )5.25
35
15 )525
 525
0
When n = 0.15,
Substitute 0.15 for n.
0.15 has two decimal
places, so multiply both
numbers by 100 to make
the divisor an integer.
5.25
n = 35.
1
A muffin recipe calls for 2 cup of oats.
3
You have 4 cup of oats. How many batches o
muffins can you bake using all of the oats
you have?
The number of batches of muffins you can
1
bake is the number of batches using the oats
Understand that you have. List the important
the Problem information:
3
The amount of oats is cup.
4
1
One batch of muffins calls for cup of
2
oats.
2
Make a Plan
Set up an equation.
3
Solve
Let n = number of batches.
3 ÷ 1 =n
4
2
3 • 2 =n
1
4
6 , or 1 1 = n
4
2
You can bake 11 batches of the muffins.
2
4
Look Back
1
One cup of oats would make two batches 2
so 1 is a reasonable answer.
Lesson Quiz
Divide.
1. 2 5
6
÷ –1
1
2
–1 8
9
2. –14 ÷ 1.25
3. 3.9 ÷ 0.65
4. Evaluate
112
for x = 6.3.
x
–11.2
6
17.7
5. A penny weighs 2.5 grams. How many pennies
would it take to equal one pound (453.6 grams)?
about 182