Transcript Multiplying and Dividing Decimals

Activator
Multiply 23 x 18.
Multiply .23 x 1.8
What is the same about both answers?
They have the same digits? 414
Multiplying and Dividing Decimals
Step 1: You do not have to line the decimals up when
multiplying.
2.36
*
5
Step 2: Multiply as normal.
2.36
*
5
The decimal in the product has
the same number of digits behind
it as the total number of digits
behind decimals in the factors.
Tell how many digits will be behind the decimal
in the answer for numbers 5-8. Do not solve:
1
3
2
2
Multiplying and Dividing Decimals
• Practice Problems:
• 8 * 1.11
• 3.26 * 123
Assessment Prompt
• Do decimals have to line up when
multiplying them?
• Thumbs up yes or Thumbs down no
• Thumbs down: you do not need to line up
the decimals. If you do you can still get the
correct answer but you don’t need to.
Dividing with Decimals
Dividing decimals by whole numbers
Dividing decimals by decimals (the
divisor must be turned into a whole
#)
Dividing Decimals
Dividing Decimals by whole numbers
Step 1: Set up the problem and then bring the decimal straight
up into the quotient.
Step 2: Divide as normal.
6.3
2 12.6
Dividing Decimals
• Do not copy: just read
• Step 3: For use with
a whole number
dividend: When you
get to the remainder
add a decimal in the
dividend and quotient.
Use zeros as place
holders. Keep dividing
8 14
Copy this only: If
dividend is a whole
number you may
need to add a
decimal and zeros
to keep going. Copy
example
EXAMPLE 1
Dividing a Decimal by a Whole Number
Soccer – Your soccer team orders sports cards for
each player. You buy a set of 8 cards for $9.92.
How much do you pay for each card?
To answer the question above about sports cards,
Find 9.92 ÷ 8.
Just click through the next
several sides. The 8 is the
divisor so all you do is set up
the problem and move the
decimal straight up.
EXAMPLE 1
Dividing a Decimal by a Whole Number
To answer the question above about sports cards,
STEP 1
Place the decimal point.
.
8)9.92
EXAMPLE 1
STEP 2
Then divide.
8 ) 9.92
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1
8 ) 9.92
8
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1
8 ) 9.92
8
1
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1
8 ) 9.92
8
19
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1.2
8 ) 9.92
8
19
16
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1.2
8 ) 9.92
8
19
16
3
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1.2
8 ) 9.92
8
19
16
32
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1.24
8 ) 9.92
8
19
16
32
32
Dividing a Decimal by a Whole Number
EXAMPLE 1
STEP 2
Then divide.
1.24
8 ) 9.92
8
19
16
32
32
0
Dividing a Decimal by a Whole Number
EXAMPLE 1
Dividing a Decimal by a Whole Number
STEP 2
Then divide.
1.24
8 ) 9.92
8
19
16
32
32
0
ANSWER
You pay $1.24 for each sports card.
Dividing Decimals
• Step 1: Dividing
decimals by decimals:
Turn the divisor into a
whole number.
• Step 2: Move the
decimal in the
dividend to the right
the same number of
places you moved in
the divisor.
3.8 43.62
Dividing Decimals
• Step 3: Bring the
decimal straight
up.
• Step 4:Divide like
normal.
38 436 .2
Stop!!
• Homework Assignment:
• Put in tracker. Textbook pg.8 #1-6. They gave
you the problems and answers. Your job is to put
the decimal in the right spot.
• Textbook pg. 9. #8, 11, 14, 17. Do not solve. Just
tell me how many numbers will be behind the
decimal in the answer.
• Example: 1.23 x .4 = 3 decimal places.
Activator
• Pair share what you remember about
dividing with decimals from yesterday.
EXAMPLE 1 Writing Divisors as Whole Numbers
Rewrite the division problem so that the divisor is a
whole number.
a. 1.83
2.5
EXAMPLE 1 Writing Divisors as Whole Numbers
Rewrite the division problem so that the divisor is a
whole number.
a. 1.83
2.5
2.5)1.83
EXAMPLE 1 Writing Divisors as Whole Numbers
Rewrite the division problem so that the divisor is a
whole number.
a. 1.83
2.5
2.5 )1.83
Multiply the divisor and
dividend by 10.
EXAMPLE 1 Writing Divisors as Whole Numbers
Rewrite the division problem so that the divisor is a
whole number.
a. 1.83
2.5
2.5 )1.83
ANSWER
18.3 25
Multiply the divisor and
dividend by 10.
Assessment Prompt
• If you have to change the divisor from a decimal
to a whole #, what else must you do?
• Will the dividend always become a whole
number?
• In this problem identify the divisor and dividend.
14.278 ÷ 5.01
Changing so divisor is a whole
number
• Change the following problems so the
divisor is a whole number.
• 15.278 ÷ 0.21
0.368 ÷ 0.2
Pair Share
• Using your dominos, you and a partner will
create an addition, subtraction,
multiplication, and division problem.
Textbook pg. 12
• #1-12.
• You are going to rewrite each problem so
that the divisor is a whole number.
• Remember rules about changing numbers
in a problem.
• #7-12 you are going to also write what you
would multiply the divisor by to make it a
whole number.