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Q
uantitative
R
easoning &
P
roblem
S
olving
356
© 2014 Pacific Crest
O
ops
! A
voiding
C
ommon
E
rrors
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Adding percents that don’t have the same base
Example
: Doug has a 10% off coupon to apply to a purchase that is on sale for 25% off. He
thinks he should get 35% off at the end, but it’s not the way the cashier rang it up.
Why?
Percents don’t add/subtract unless they are percents of the same base amount. In this
case the 25% is taken off the original price, but the 10% is taken off the resulting sale
price, not the original. So the percents can’t add.
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Dividing the wrong way or interpreting a unit price incorrectly
Example
: A box of cereal costs $5.39 for 24 ounces and $3.75 for 16 ounces. Joan calculated
24
÷
5.30 = 4.45 and 16
÷
3.75 = 4.26, so she bought the 16 ounce box as the better
buy.
Why?
Calculating price per ounce (price divided by ounces) or ounces per dollar (ounces
divided by price) makes a difference in which way the results are to be compared.
In one case the lower result is the better buy, while in the other case, it’s the higher
result.
A
re You Ready?
Before continuing, you should be able to ...
I can...
OR
Here’s my question...
calculate the result of successive percent
discounts
calculate the percent markup of an item,
given the original cost and final price
find the unit price of an item
calculate the price, including sales tax, of
an item
P
lan
How to complete the activity
1. Read Model 1.
2. Apply the methodology to the scenario in Model 2, working in groups or teams. Use appropriate
formulas to calculate and validate your results. (There is a blank methodology form available on the
companion website.)
3. Read and answer the Critical Thinking Questions.
4. Complete the remainder of this activity (from Demonstrate Your Understanding through Assessing
Your Performance) on your own, or as directed by your instructor.