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Say you had a problem like this: |
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3 + 4
× 6 |
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before you say 42, you need to know a special
rule: |
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MULTIPLICATION GETS
DONE
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BEFORE
ADDITION
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That means first we multiply: |
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4
× 6 =
24
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Then we add: |
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3 + 24 =
27
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OK, Fine. Do x before +.
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Are there any other
things like that to remember? |
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A few: |
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MULTIPLICATION GETS
DONE
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BEFORE
SUBTRACTION
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So if we have: |
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2
× 6 -
3
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First we multiply: |
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2
× 6 =
12
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Then we subtract |
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12 - 3 =
9
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DIVISION GETS
DONE
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BEFORE
ADDITION
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So if we have: |
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3 + 10 ÷
2
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First we divide: |
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10 ÷ 2 =
5
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Then we add: |
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3 + 5 =
8
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DIVISION GETS
DONE
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BEFORE
SUBTRACTION
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So if we have: |
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6 ÷ 3 -
2
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First we divide: |
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6 ÷ 3 =
2
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Then we subtract: |
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2 - 2 =
0
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Think of multiplication and Division as the big shots. |
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They go first. |
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Addition and subtraction follow along after. |
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Swell. Let's put that all together in one
sentence: |
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MULTIPLICATION AND
DIVISION
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COME
BEFORE |
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ADDITION AND
SUBTRACTION. |
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OK, That's fine. But what do we do with this
puppy? |
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2
× 6 ÷
4
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Multiplication and Division are equal big shots. |
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Which
goes first? |
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The rule for stuff like this says: |
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WHEN YOU HAVE
SIGNS OF EQUAL
IMPORTANCE,
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GO LEFT TO
RIGHT
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So we do |
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2
× 6 =
12
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Then we do: |
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12 ÷ 4 =
3
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Addition and subtraction work the same way. |
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Just go left
to right. |
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Example: |
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2 - 6 +
5
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First subtract: |
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2 - 6 = -
4
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(oh no! not a negative
number!)
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Then add: |
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- 4 + 5 =
1
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Now
let's do a nasty one. |
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Example: |
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3
×
5 - 2 + 4 - 6 ÷
2
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The multiplication and division get done
first: |
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3
× 5 =
15
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- 6 ÷ 2 = -
3
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(remember, the signs are different so
the answer is negative)
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Now the problem looks like this: |
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15 - 2 + 4 -
3
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What's left is all addition and subtraction so just go
left to right: |
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15 - 2 =
13
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13 + 4 =
17
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17 - 3 =
14
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copyright 2005 Bruce Kirkpatrick |
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