Transcript PowerPoint: Writing Alegebraically

Writing Equations
to solve
Word Problems
One way to solve word problems is to
look for key words to help you write
an equation.
You must decide what the variable
represents – it should be what you are
trying to find!
Here are two sample word problems
and solutions:
You have a suitcase that can hold
up to 23 kilograms. You are
packing clothes and want to make
sure you have space left over for a
PlayStation you plan to buy before
your trip. If the PlayStation
weighs 3.75 kg, how many clothes
can you pack?
Let x = amount of clothes
Clothes + Playstation =
x
+
3.75
Total weight
=
- 3.75
- 3.75
x
23
=
19.25 kg
John is 3 years less than
twice his sister’s age. If
John is 11, how old is his
sister?
Let s = sister’s age
John’s
age
11
=
3 years less
than
twice his
sister’s age
2s
-3
Note: A common key word that indicates where
to put the equal sign is the word ‘IS’ 
Another way to solve word problems
is to organize the information.
For example, you may find it useful to
create a table.
Here is a sample word problem and
solution:
Here is a table with information from the first
sentence filled in algebraically.
Now information from the second sentence is
included algebraically.
An equation is written from the information in the
table.
Finally, solve the equation to find the answer:
h + 8 + 5 = 2 ( h + 5)
h + 13 = 2h + 10
-h
-h
13 = h + 10
-10
-10
3=h
Therefore, Chuck is 3 and Cara is 11!
Try this strategy!
Cross out with pencil (or highlight) the information as
you use the information in your chart or diagram.
Highlight (in a different color) what is left and use this to
write your equation.
Solve the equation and answer the problem.
Write equations for the
following problems on
a white board.
Check your answers
on the following slide.
Seven more than
three times a
number is 31
7 + 3n = 31
The quotient of
a number and 9
increased by 3
is -7
n
+ 3 = -7
9
The width of a singles
tennis court is 27
feet. This is one foot
more than one-third
of the length.
1
27 = 1+ l
3
Joanne starts with $5 in her
savings account and adds
$10 every week. Write an
expression with a variable
that tells how much she will
have in her account after n
weeks.
5 +10n
How much will Joanne have
in her savings account after 9
weeks?
5 +10(9)
5 + 90
$95