Transcript 15-Minute Math: Decimals

15 Minute Math
This presentation will review different math skills that will help you
with every day math problems.
Each lesson takes approximately 15 minutes to do. Almost anyone
can find an extra 15 minutes out of his or her day, whether it be
during breakfast or right before bed. In just under 3 weeks, you
can review all the TABE Computation Math sections.
Look for the Professor. He has special hints to help make
working the math problems faster and easier.
15 Minute Math

Decimals
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Lesson 5 – What Are Fractions?
Lesson 6 - Addition & Subtraction (no
whole #s)
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Lesson 7 – Addition & Subtraction
(with whole #s)
o
Lesson 8 – Multiplication & Division
Percentages
o
Lesson 9 – Converting Decimals to
Fractions to Percents
o
Lesson 10 – Calculating the Part
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Lesson 11 – Cross-Multiplication
Method
Integers
o
Fractions
o
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Lesson 1 – What Are Decimals?
Lesson 2 – Addition & Subtraction
Lesson 3 – Multiplication
Lesson 4 – Division
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Lesson 12 – Addition & Subtraction
Lesson 13 – Multiplication, Division, &
Absolute Value
Algebra
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Lesson 14 – Adding & Subtracting
Variables
o
Lesson 15 – Multiplying & Dividing
Variables
o
Lesson 16 – Square Roots
Order of Operations
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Lesson 17 – Please Excuse My Dear
Aunt Sally
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Lesson 18 – Order of Operations with
Variables
Practice Tests
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Lesson 19 – Practice Test #1
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Lesson 20 – Practice Test #2
15 Minute Math – Decimals
Lesson # 1 – What Are Decimals?
This lesson explains how to
read and work with decimals.
Problem: You work in a medical lab and you need to tell your coworker how
much medicine you need.
“I need two tenths of a gram of insulin.”
Saying numbers correctly can ensure everyone is talking about the same
thing.
15 Minute Math – Decimals
Lesson # 1 – What Are Decimals?

Decimals are numbers that are less than 1 but greater than 0
0 < 0.1 < 1 (0.1 is between 0 and 1, so it is a decimal)

They appear to the right of the decimal point
whole number
decimal
39.1
“39” is the whole number part
“.1” is the decimal part

“39.1” is read…
“Thirty-nine and one tenth”
 “0.1” is the same thing as
“.1”. “.1” is just a lazy way of
writing the number.
15 Minute Math – Decimals
Lesson # 1 – What Are Decimals?
1
+
+
+
+
+
+
+
+
10,000.
2,000.
300.
40.
5.
.6
.07
.008
.0009
12,345.6789
2
3
4
5
6
7
8
9
The “3” is in the hundreds column,
 Remember, decimals
so there are “3 hundreds”.
have a “th” at the end
If all the other numbers were
of their names.
a 0, then the number would be
00300.0000, which is 300 (three hundred.)
The “7” is in the hundredths column,
so there are “7 hundredths.”
If every other number were a 0, then the number
would be 00000.0700, which is 0.07 (seven hundredths.)
15 Minute Math – Decimals
Lesson # 1 – What Are Decimals?
To read a number…
For example: 20.045 is read, “Twenty and forty-five thousandths.”
 Extra zeroes to the far right of a
decimal don’t change the value, but
they do change how you pronounce
the number.
0.2 = 0.20 = 0.200 but…
0.2 = “two tenths”
0.20 = “twenty hundredths”
0.200 = “two hundred thousandths“
15 Minute Math – Decimals
Lesson # 1 – What Are Decimals?
Try it yourself
What numbers are these?
Three and two hundredths = 3.02
Forty and two thousandth =
Twelve and twelve hundredths =
Eighty and eighty ten-thousands =
How do you say these numbers?
37.03 = Thirty-seven and three hundredths
9.04 =
20.040 =
100.01 =
Which of these are true:
A) 2.01 = 2.010
C) 2.001 = 2.100
E) 2.10 = 2.100
End of Lesson 1
B) 2.01 = 2.001
D) 2.10 = 2.010
F) 2.0010 = 2.001
Click for answers:
Forty and two thousandth = 40.002
Twelve and twelve hundredths = 12.12
Eighty and eighty ten-thousands = 80.0080
9.04 = nine and four hundredths
20.040 = twenty and forty thousands
100.01 = one hundred and one hundredth
A, E, and F are true
15 Minute Math – Decimals
Lesson # 2 – Addition & Subtraction
This lesson explains how to add and subtract
numbers that have a decimal point.
Problem: You need to take 3 grams of pain medication. You’ve already
taken 0.75 grams of pain medication from a multi-purpose formula. How
much more medication do you need?
3.00
-0.75
2.25
When adding and subtracting numbers with decimal points, ALWAYS line up
the decimal points!
15 Minute Math – Decimals
Lesson # 2 – Addition & Subtraction
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
Line up the decimals points
Put zeroes in the blank spaces to help you see what you’re
adding
24.3 + 18.45

1
24.30
+18.45
42.75
18.62 – 3.8

7 1
/
18.62
- 3.80
14.82
 When adding, don’t forget to carry when numbers add
up to more than 10.
 When subtracting, don’t forget to borrow if the top
number is smaller than the bottom number.
15 Minute Math – Decimals
Lesson # 2 – Addition & Subtraction

All numbers have a decimal point, even if you can’t see it.
For example, $15 can also be written as $15.00
20 + 4.02
 20.00
+ 4.02
24.02
100 – 25.783
Remember when you’re borrowing, you
can’t borrow from nothing (zero). Make
sure you borrow all the way over to the
first non-zero number you find.

99
9 9
1
100.000
/// //
- 25.783
74.217
 Even if you don’t
see the decimal point,
it’s actually at the end.
100 = 100. = 100.00
15 Minute Math – Decimals
Lesson # 2 – Addition & Subtraction
Try it yourself
2.89 + 1.5 =
20.6 + 10.9 =
3.13 + 9 =
20 + 8.2 =
9.373 + 3.34 =
9 + 2.8 =
12.99 – 8.1 =
19 – 3.2 =
2.933 – 1.2 =
8.4 – 5.555 =
20 – 2.5 =
100 – 2.66 =
End of Lesson 2
Click for answers:
2.89 + 1.5 = 4.39
20 + 8.2 = 28.2
12.99 – 8.1 = 4.89
8.4 – 5.555 = 2.845
20.6 + 10.9 = 31.5
9.373 + 3.34 = 12.713
19 – 3.2 = 15.8
20 – 2.5 = 17.5
3.13 + 9 = 12.13
9 + 2.8 = 11.8
2.933 – 1.2 = 1.733
100 – 2.66 = 97.34
15 Minute Math – Decimals
Lesson # 3 – Multiplication
This lesson explains how to multiply numbers that
have a decimal point.
Problem: You need to buy 12 cans of paint costing $5.29 each. How much
will you pay?
5.29
× 12
63.48
When multiplying numbers with decimal points, count the total number of
numbers to the right of the decimal point in the problem and make sure
the answer has the same number!
15 Minute Math – Decimals
Lesson # 3 – Multiplication
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
Don’t worry about the decimal until you’re done multiplying
everything
First multiply, and then count up the places to the right of the
decimal point and put the decimal in the answer.
3.51 x 1.4  351
×14
1404
3 decimal
+3510
places
4914  4.914
So, 3.51 x 1.4 = 4.914!




first, multiply 351 by 4
then, multiply 351 by 10
then, add up the numbers
last, since there are a total of 3
decimal places in the problem,
start from the right and move the
decimal 3 places to the left in the
answer (the problem has 3
decimal places and so does the
answer)
15 Minute Math – Decimals
Lesson # 3 – Multiplication

Remember to only count numbers to the RIGHT of the decimal
point.
2.3 × 0.0002  23
×2
46  0.00046
5 decimal
places
5 decimal
places
So, 2.3 x 0.0002 = 0.00046!

Sometimes you may see
.00046 instead of
0.00046. Both are
right, but it’s more
common to put a 0 in
the ones place.
15 Minute Math – Decimals
Lesson # 3 – Multiplication

There are some shortcuts you can take if you’re multiplying by a
multiple of 10. Multiples of 10 are things like 10, 100, 1000 and
also things like 0.1, 0.01, 0.001, etc.
shift the decimal left 4 places (if you
(don’t see the decimal point it’s at the end)
297 × 0.0001 = 0.0297
4 decimal
places
move the decimal point right
2 spaces (100 has 2 0’s)
2.309 × 100 = 230.9
Try not to think about if you’re moving the
decimal to the right or the left. Think if you need
to make the number larger (because you’re
multiplying by a number bigger than 1) or if you
need to make the number smaller (because you’re
multiplying by a number between 0 and 1). Then
move the decimal point in the direction that will
make the number bigger or smaller.
15 Minute Math – Decimals
Lesson # 3 – Multiplication
Try it yourself
27.2 × 9.2 =
3.2904 × 0.22 =
62.5 × 12.8 =
38 × 0.25 =
0.034 × 0.026 =
8.02 × 2.1 =
2.04 × 0.001 =
589 × 100 =
10.2 × 1.2 =
0.34 × 0.5 =
5.89 × 100 =
9.9999 × 0.01 =
Click for answers:
End of Lesson 3
27.2 × 9.2 = 250.24
38 × 0.25 = 9.5
2.04 × 0.001 = 0.00204
0.34 × 0.5 = 0.17
3.2904 × 0.22 = 0.723888
0.034 × 0.026 = 0.000884
589 × 100 = 58,900
5.89 × 100 = 589
62.5 × 12.8 = 800
8.02 × 2.1 = 16.842
10.2 × 1.2 = 12.24
9.9999 × 0.01 = 0.099999
15 Minute Math – Decimals
Lesson # 4 – Division
This lesson explains how to divide numbers that
have a decimal point.
Problem: A wall measures 96.5 inches tall. You need to install 3.25 inch tall
siding panels. How many panels do you need?
26.5
3.25|96.5
When dividing numbers with decimal points, decimal point placement is key.
15 Minute Math – Decimals
Lesson # 4 – Division

Remind yourself of the steps you need to take when dividing
1.
Divide
8
8203
21|172263
2.
Multiply
3.
Subtract
4.
Bring down one
more number
and do it again
8
21|172263
-168
8
21|172263
-168
4
8
21|172263
-168
42
21|172263
-168
42
-42
06
- 0
63
-63
0
15 Minute Math – Decimals
Lesson # 4 – Division
Step 1 - Move the decimal of the divisor (outside the house) as far to
the right as you can
Step 2 - Move the decimal of the dividend (inside the house) by the
same number of spaces
Step 3 - Move the decimal straight up onto the answer line
Step 4 - Divide like normal
Problem
Steps 1 & 2
Step 3
.
 33 |89.1
Step 4
2.7
8.91 ÷ 3.3  3.3 |8.91  33 |89.1
 33 |89.1
- 66
231
 Think of the division sign, | , like a house. With all division
problems, the first number goes inside the house (the 8.91) and the
- 231
second goes outside the house (3.3).
0
 If you forget, think about a problem you know. 10 ÷ 2 = 5. You
wouldn’t say 10 | 2. To work it out you’d say 2 |10 (2 goes into 10.)
15 Minute Math – Decimals
Lesson # 4 – Division
Problem
Steps 1 & 2
8.91 ÷ 0.33  0.33 |8.91  33 |891.
Step 3
.
 33 |891.
Move the decimal 2 places to the right
Problem
Steps 1 & 2
Step 3
Step 4
27.
 33 |891.
- 66
231
- 231
0
Step 4
.
2700.
8.91 ÷ 0.0033 0.0033 |8.91  33 |89100.  33 |89100.  33 |89100.
- 66
Move the decimal 2 places to the right
231
Fill in the empty spaces with zeroes
- 231
0
15 Minute Math – Decimals
Lesson # 4 – Division
Try it yourself
3.2 ÷ 64 =
60.8 ÷ 19 =
187.53 ÷ 3 =
3.2 ÷ 6.4 =
60.8 ÷ 0.19 =
187.53 ÷ 0.03 =
32 ÷ 6.4 =
0.608 ÷ 0.19 =
18753 ÷ 0.3 =
32 ÷ 0.00064 =
608 ÷ 1.9 =
0.0018753 ÷ 0.3 =
End of Lesson 4
Click for answers:
3.2 ÷ 64 = 0.05
3.2 ÷ 6.4 = 0.5
32 ÷ 6.4 = 5
32 ÷ 0.00064 = 50000
60.8 ÷ 19 = 3.2
60.8 ÷ 0.19 = 320
0.608 ÷ 0.19 = 3.2
608 ÷ 1.9 = 320
187.53 ÷ 3 = 62.51
187.53 ÷ 0.03 = 6251
18753 ÷ 0.3 = 62510
0.0018753 ÷ 0.3 = 0.006251