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That first lesson was easy! Let's try
some harder ones that involve two steps! But first you have to
review some rules called
Order of Operations. Take this problem:
3 + 5 x 8
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Rachel solves it like this:
3
+ 5 x 8 =
8 + 8 = 16
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Ricky solves it like this:
3
+ 5 x 8 =
3 + 40 = 43
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They both look
right? |
But you know
only one can be correct, so which one is it???? |
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Lucky for us, someone did make
some rules which everyone in the world needs to follow!
Remember from a previous lesson that this set of rules is called
Order of
Operations. Remember
Please Excuse My Dear
Aunt Sally?????
Well she is back, and you will use her again in evaluating
Algebraic Expressions! Do you need to review that lesson?
If so
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After that quick review, you know Ricky is right because
Multiplication must be done before addition.
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So if you have an expression with two operations
(2y + 5), use your Order of
Operations knowledge to solve it correctly.
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Step One:
If the variable is : |
Step Two:
Substitute it in the expression
2y + 5 |
Step Three: Multiply first because of Order of
Operations.
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Step Four: Then do
addition to get answer |
| y
= 2 |
2(2) + 5 |
4
+ 5 |
4
+ 5 = 9 |
| y = 4 |
2(4) + 5 |
8 + 5 |
8 + 5 = 13 |
| y
= 0 |
2(0) + 5 |
0
+ 5 |
0
+ 5 = 5 |
| y = 7 |
2(7) + 5 |
14 + 5 |
14 + 5 = 19 |
OK, that was easy; let's try some more difficult
ones, and in slightly different forms.
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Step One:
If the expression is: |
Step Two:
and the variable is: |
Step Three:
do first operation (according to Order of
Op) |
Step Four:
do second operation (according to Order of
Op) |
Step Five:
Solve |
|
2y -3 |
y = 6 |
(multiply first)
2(6) -3 |
(subtract 2nd)
12 -3 |
12 -3 = 9 |
| m ÷
6 + 4 |
m =
12 |
(divide first)
12 ÷ 6 + 4 |
(add second)
2 + 4 |
2 + 4 = 6
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3x + 4 |
x = 1.5 |
(multiply first)
3(1.5) + 4 |
(add second)
4.5 + 4 |
4.5 + 4 = 8.5 |
| 2t
÷ 5 |
t =
10 |
(multiply first)*
2(10)÷ 5 |
(divide second)*
20 ÷ 5 |
20 ÷ 5 = 4 |
|
100n + 2 |
n = 0 |
(multiply first)
100(0) + 2 |
(add second)
0 +
2 |
0 +
2 = 2 |
* When both
multiplication and division are in the expression, go from left to
right.
Now what would you like to do?
Go back to
Lesson
Part 1?
or go to
Practice 1?
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