Transcript Lesson 4.2 Adding and Subtracting Decimals

Lesson 3.3
Adding and Subtracting Decimals
Essential Question:
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How do I add and subtract decimals?
Always line up decimals
Add and subtract like you always do
Bring decimal straight down in your answers
Adding
Examples:
4.55 + 11.3
Put the first number on
the top of the second
number and line up the
decimals.
You can
add a zero
to help
4.55
keep
+ 11.30
everything
lined up
15.85
When adding
or subtracting
you always
start from the
right and work
left.
6.44 + 16
When there is
not a decimal
put one
behind the
number.
Line up
the
decimal
6.44
+ 16.0
22.44
Add a zero to
line up
everything
-8.33 + -10.972
Line up
the decimal
-8.33
+
-10.972
0
-19.302
Add a zero to
line up
everything
Same signs
Add – keep
the sign
Subtracting
Examples:
5.34 -2.08
Put the first number on
the top of the second
number and line up the
decimals.
5.34
-2.08
3.26
Different signs
Take difference
-38.59 – (-7.81)
+
Line up
the decimal
-38.59
+ 7.81
-30.78
Subtract to
add when
negatives are
used.
Different signs
take
difference
28 – 15.911
When there
is
not a decimal
put one
behind the
number.
7 99
28. 000
-15.911
1 2.0 8 9
Add zeros to
line up
everything,
then
subtract
Magic Square
0.5
7
4.625
8.75
The sum of each
row, column,
and diagonal
must be the
same.
6.375
0.5
7
5.25
4.625
4
2.25
8.75
2.875
Sums to
13.875
Estimation
• You can always estimate to know if your answer is
close.
• 6.7 + 8.2 =
7
• Ask yourself, “Is 6.7 closer to 7 or 6?”
• Ask yourself, “Is 8.2 closer to 8 or to 9?”
8
• Your estimate is 7 + 8 = ________
• Actual answer?? _______________
Estimate and solve the following…
(E = Estimate, A = Actual)
Watch the
signs!!
8.9 + 3. 4 E=______ A = _______
7.4 – 2.1 E= ______ A = _______
6.7 – 4.3 E= ______ A = _______
2.9 + 1.8 E= ______ A = _______
Ms. Kim is making 3 different kinds of cookies using
chocolate chips. The recipes ask for
2.25 kg, 1.75 kg, and 4.55 kg of chocolate chips.
Ms. Kim has 11 kg of chocolate chips total.
a) Estimate to find out how much Ms. Kim needs.
Then find the actual amount.
b) Does she have enough to make the cookies?
c) If your answer is “NO”, how much more does
Ms. Kim need to make the cookies? If your
answer is “YES”, how much does she have
leftover?