Girlfriends Shopping Adventure

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Girlfriends Shopping Adventure
2

• One afternoon, Joan and Lisa went to the mall
  shopping. Lisa was looking for a new outfit to
  wear to a friends party this weekend. She
  wanted a new pair of jeans and a nice stylish
  top. As they walked by Hot Topic, they saw in
  the window display a pair of really cool jeans.
  They decided to go in and check out the price.
  The jeans were originally 69.99 and with a tag
  that said, Take an additional 25 off. Lisa
  said, I only have 55.00 on me. Is this
  enough money to buy the jeans?

3
Understanding the Problem

• Lisa wants to know if she has enough to buy a
  pair of jeans, and maybe a top as well
• Important facts
• Jeans original price 69.99
• Now on sale for 25 off
• Lisa has 55.00 to spend

4
Coming Up With a Plan

• We can do this in our heads. Heres what we can
  do
• First well round 69.99 to 70.00 to estimate
  25 of the price more easily.
• Then well subtract the 25 discount from the
  original price.
• Then well subtract the reduced price from the
  55.00 Lisa has to see if she will have enough
  money.

5
Carrying Out the Plan

• First, we found out 25 of 69.99 by using mental
  math. To make it simpler, we rounded 69.00 to
  70.00. 25 can be split into 10,10, 5
  easily. To get 10 off we moved the decimal
  point 1 place to the left which gave us 6.99 or
  7.00 if we round it. To get 5 off we just took
  ½ of 7.00 which is 3.50 because 5 is ½ of 10.
  We rounded 3.50 to 4.00 to make it easier to add
  in our heads. Then we added to get the total
  amount of the discount.
• 10 of 70.00 7.00
• 10 of 70.00 7.00
• 5 of 70.00 3.50 (4.00 rounded up)
• 25 of 70 18.00 discount

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Next, we took the discount and counted up to the
rounded amount of the original price of the
jeans. This gave us the sale price. 18.00
(discount) 2.00 (counting up)
20.00 20.00 50.00 (counting up) 70.00
(original amount of jeans).
2.00 50.00 52.00 (sale
price) Finally, we took the sale price and
counted up to the amount Lisa had to spend. This
let us know if she had enough money to buy the
jeans and if any money was left over for the top.
52.00 (sale price) 3.00 (counting up)
55.00 (amount Lisa had) This
left about 3.00 left over to spend on a top.
7
Looking Back

• We knew Lisa had enough to buy the jeans because
  we estimated that 25 off 70.00 was 18.00,
  nearly 20 off the original price of 70.00.
  20.00 from 70.00 equals 50.00 which is close
  to our sale price of about 52.00. So, we know
  our answer sounds correct.

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So, we figured Lisa had enough money to buy the
jeans, but unfortunately, she did not have enough
money to buy a new top. Joan said, Would you
like to borrow some money from me? I will lend
it to you for a fee plus interest will be
charged. Do you want to try and figure that one
out? Joan just laughed. Lisa said, Since when
do we have to do math on our day off, especially
when we are out shopping? Well, she said, I
guess our teachers do know what they are talking
about, Math is EVERYWHERE!
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Credits

• Joan Siniavsky and Lisa Sanderlin
• January 2007