SME
Grade 7 Math · Ratios & Proportions
Tax, tip, markup, discount and percent change
Use this for “Add a 7.5% sales tax to a $40 price. What is the total?” and tips and markups.
Diagram
7.5% of $40 = $3
$40 + $3 = $43
This is an example. Type your own values to start a new problem.
p
%
of
$
w
=
$
c
$
w
+
$
c
=
$
T
Formulas
c
=
w
×
p
÷
100
(amount
added
=
price
×
percent
added
÷
100)
3 = 40 × 7.5 ÷ 100
T
=
w
+
c
(total
=
price
+
amount
added)
43 = 40 + 3
T
=
w
×
(100
+
p
)
÷
100
(total
=
price
×
(100
+
percent
added)
÷
100)
43 = 40 × (100 + 7.5) ÷ 100
Assumptions
•
The price is 100%. The tax, tip or markup is p% of it.
•
The total is 100% + p% of the price.
•
Sales tax, a tip and a markup all add a percent of the price.
•
Round money to the nearest cent.
Step-by-step
WE KNOW
w = $40 (price), p = 7.5% (percent added)
FIND
amount added (c), total (T)
Step 1 · Find amount added (c)
Use c = w × p ÷ 100 (amount added = price × percent added ÷ 100)
The
amount
added
is
p
%
of
the
price.
c
=
40
×
7.5
100
c
=
300
100
c
=
$3
Step 2 · Find total (T)
Use T = w + c (total = price + amount added)
Add the amount added to the price.
T
=
40
+
3
T
=
$43
Check
Put the numbers back in. Both sides should match.
3 = 40 × 7.5 ÷ 100 ✓
43 = 40 + 3 ✓
43 = 40 × (100 + 7.5) ÷ 100 ✓
Topic check
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