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Lesson 3.3 Adding and Subtracting Decimals. Essential Question:. 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. - PowerPoint PPT Presentation
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Lesson 3.3 Adding and Subtracting Decimals
Essential Question:
• 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.
4.55 + 11.3
You can add a zero
to help keep
everything lined up
0 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 onebehind thenumber.
Line up the
decimal 6.44 + 16.
Add a zero to line up
everything
22.440
-8.33 + -10.972
-8.33 -10.972
Same signsAdd – keep
the sign
Add a zero to line up
everything0Line up
the decimal
-19.302+
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 signsTake difference
-38.59 – (-7.81)
-38.59 + 7.81
Subtract to add when
negatives are used.
Different signs take
difference
Line upthe decimal
-30.78
+
28 – 15.911
When there is
not a decimalput one
behind thenumber.
28. -15.911
Add zeros to line up
everything, then
subtract
0007 9 9
80.21 9
0.5 7
4.625
8.75
Magic Square
6.375 0.5 75.25 4.625 42.25 8.75 2.875
The sum of each row, column, and diagonal must be the
same.Sums to 13.875
Estimation• You can always estimate to know if your answer
is close.
• 6.7 + 8.2 =
• Ask yourself, “Is 6.7 closer to 7 or 6?”• Ask yourself, “Is 8.2 closer to 8 or to 9?”
• Your estimate is 7 + 8 = ________
• Actual answer?? _______________
7
8
Estimate and solve the following…(E = Estimate, A = Actual)
8.9 + 3. 4 E=______ A = _______
7.4 – 2.1 E= ______ A = _______
6.7 – 4.3 E= ______ A = _______
2.9 + 1.8 E= ______ A = _______
Watch the signs!!
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?
