11. Percentages: 50% More Fun!

You can have 50% of the fun…or 50% more fun…or half as much fun…or even half-again as much fun. Are these all the same?  They all use 50% or the word "half", but the slight addition of a few different english words changes the meaning drastically.   

Half or 50% of the Fun is giving you 50% of the total - hence you are enjoying this post only half as much as you could.

However, 50% more Fun or Half again as much Fun are providing words that imply adding more to the total.  In this case, you are giggling all of what I would expect, plus another 50% to make a total of 150% total giggling.

In a previous post on Rates, I wrote that Percentages always add up to 100%.  Well, I must have been smokin’ something.  Of course you can have a Percentage more than 100%.  By simply reading this post, you are having 50% more, or 150% of the Fun compared to other people who are having only 100% of the fun reading some other lame math post.   

Let’s try another example of percentages greater than 100%.  You want to borrow $100 from me..and you agree to pay me back the $100 by the end of the week plus an additional 20% interest (I have a friend Guido who will make sure you do).  I stand to realize 120% gain on my investment:  100% being the total amount I loaned to you paid back plus an extra interest of 20%.   

When word problems use standard percentages like 30% or 25%, it is assumed that they are using 100% as the total.  It is the whole pie.  100%.  You cannot have more than the whole pie...unless of course they add more pie to the problem.  My $100 I loaned to you was the 100%.  When I asked for an additional 20% interest, I just added more pie.

Often, word problems will tell us the total amount (the 100%) and ask you to solve for a missing percentage.  For example, there are 30 children in the classroom (Whoa - see what happened there??  It just defined the total...the 100%), and there are 20% boys.  What is the percentage of girls in the class?  In this case, they must add up to 100%.  Obviously the percentage of Girls in the class is 80% (100% - 20% = 80%).  

One last fun point on Percentages.  Common Core may require the ability to describe percentages in a variety of forms.  The tests may provide one form, and ask to define the other forms: 

Percent Fraction:  It is the percent, but instead of showing the “%” sign, we show the number divided by 100.

Percent:  It is the same number as used in the Percent Fraction above except followed by the “%” sign instead of dividing by 100.  Think of the “%” sign meaning “divided by zero”.

Fraction:  One number over another number usually defined in its lowest possible form (i.e. write 1/4 instead of 2/8).  This fraction would be the same as Percent if you were to divide the top number by the bottom number.  For example:  1/4 is the same as 0.25 if you divided the number 1 by the number 4.  

Decimal:  The Decimal number is the same as the Percent Fraction number if you divided the top number by 100.  For example, 0.25 is the same as 25/100.

Below is a table showing some examples of the various forms.

Boy-oh-boy could we have more fun with Percentages?  I think not!  Maybe I should have labeled this Post as 75% more fun.

10. Answers to Tape Diagrams

Answer to Tape Q1:

The ratio of pepperoni to sausage is 3 to 1.  We used up 24 slices of pepperoni.  How many pieces of sausage did we use?

We can see from the problem that the ratio is 3:1.  So we need three boxes and one box.  We also know the total Pepperoni is 24.  So set up the Tape diagram with what we know: 

Next:  figure the magic number (remember:  all of the numbers inside the boxes must be the same). What goes into 24 equally three times?…why the number 8 of course.  Write the number 8 in all of the boxes.   

Now calculate the quantity of sausage used (Hmmm, let’s see…. 1 times 8 = 8!!!).

Answer to Tape Q2:   It’s Pizza Day at the cafeteria Can’t get enough of that Pizza).  There are two cafeteria lines - Sixth graders in one line and Fifth graders in the other.  There are two Sixth graders for every three Fifth graders.  You count 40 Sixth graders in your line.  How any Fifth graders are in line?

Set up the Diagram with what we know:  

•  A ratio of 2:3 (sixth graders to fifth graders).  Hence show two boxes and three boxes.  Label the three-box row "fifth graders" and the two-box row "sixth graders”.
• We also know the number 40 for the total sixth graders - so 40 on the sixth grade line.  Your diagram should now look like this: 

Next:  Find the magic number:  Two sixth graders boxes add up to 40.  The magic number must be 20 (40 divided by 2).   Now write 20 in all of the boxes.

Add up the number of “20s"in the fifth grade boxes and write the total in the fifth grade line on top (which should be 60).   Voila. 

Answer to Tape Q3:  You have major math homework tonight - 30 math problems…YIKES!.  You are also starving for those homemade Chocolate Chip cookies.  Mom says you can have two cookies for every 6 math problems you work out correctly.  You finish all of the math homework correct.  How many cookies do you get?

What do we know?

• The Ratio is 2 cookies to 6 Math, or 2:6.  (hence two boxes and six boxes)
• The bonus number is the total Math problems at 30.

Set up the diagram: 

Now solve for the magic number.  Six equal boxes adding up to 30.  (30 divided by 6 = 5).  Write “5" in all of the boxes.

  The quantity of cookies is 10.

9. Get it on Tape (Diagrams)

Tape Diagrams are yet another method for graphically or visually solving ratio-type word problems. It is slightly different than Double Lines or Equivalence Tables.

Tape-type word problems typically include a ratio of two things (two of These to three of Those) plus a bonus of one other number which is typically the total of one of the items.  For example:  The ratio of Apples to Oranges is 4:3.  We have 24 Apples….how many Oranges do we have?  See?  What did I tell you?  This problem gave us the ratio of the two items plus a bonus number of the total of one of the items.

When you set up a Tape Diagram for this type of problem, you simply show the ratio in the form of a bunch of boxes (it’s supposed to resemble some sort of  piece of tape).  

The drawing at right shows two Tape Diagrams, one for a ratio of 3:2 and the other a ratio of 4:3.   

To diagram the 4:3 ratio of apples-to-oranges problem above, we would draw four boxes in a row to resemble the apples, and then three boxes in a row for the oranges. 

Important Safety Tip:  Always make the boxes the same size, and always line them up on the left.

Next, label the rows of boxes.  We can also add the bonus number we know, which from the problem is 24 apples.  Show that number across the top of the Apples. 

The problem is asking for the total number of Oranges…which is the bottom number.

Now here’s the tricky part:  We want to place a number in all of the boxes, and that “magic" number will be the same number in all boxes.  There is only one number which fits (that’s why it is a magic number).  To figure out that one magic number, we look at the row of boxes for the item which we know the total number - in this case it is the total of 24 apples.  Since we have four boxes, and the number is always the same number in all boxes, we divide (in our head) the total of 24 by the number of boxes in that row (4).  

Another way to think of this is:  you have a total of 24 apples in a pile.  You need to put an equal number of apples in each of the four boxes.  You start by putting  one apple in each box and keep repeating until all of the apples are gone.  You would end up with 6 apples in each box.  Hence,  24 divided by four is six.  So the magic number is 6.

Now here’s the fun part: Since the magic number is 6, put a "6" in each of the Oranges boxes.  There are 3 boxes of 6. 

So, again, we do in our head “3 times 6 equals 18” , and write 18 in the bottom total for Oranges.

Another important safety tip:  These types of Tape Diagram problems always lend themselves to using numbers which are easily divisible by other numbers.  We usually do not see a ratio of 4 1/2 to 3 (where it’s tough to draw four and half boxes on top), or a ratio of 4:3 with a total of 23 (where 4 doesn’t divide into 23 very easily).  

Now try a few problems (answers to follow in another follow-on post):

Tape Q1:  We’re making pizza!  The ratio of pepperoni to sausage is 3 to 1.  We used up 24 slices of pepperoni.  How many pieces of sausage did we use?

Tape Q2:   It’s Pizza Day at the cafeteria (can’t get enough of that Pizza).  There are two cafeteria lines - Sixth graders in one line and Fifth graders in the other.  There are two Sixth graders for every three Fifth graders.  You count 40 Sixth graders in your line.  How any Fifth graders are in line?

Tape Q3:  You have major math homework tonight - 30 math problems…YIKES!.  You are also starving for those homemade Chocolate Chip cookies.  Mom says you can have two cookies for every 6 math problems you work out correctly.  You finish all of the math homework correct.  How many cookies do you get?

Good Luck!

8. Answers to Double Lines

Answer to Double Line Problem #1:

There are 20 girls in the class, and the ratio of Girls to Boys is 4:3.  How many Boys?
Draw the two parallel lines & label one "Girls"and other "Boys".

We are solving for Boys, so start with Girls.  Since there are "4" Girls per whatever and a total of 20 Girls, draw a series of vertical lines and label each one with increments of 4 (on the Girls line) until you get to 20.

Next: Since for every 4 Girls there are 3 Boys, we are going to use increments of 3 on the Boys line. Under the Girls "4", write a "3" on the Boys line, then a "6" under the Girls "8", then "9", "12", and finally "15" under the Girls "20".  Your Line Diagram should look like this:

There answer is 15.


Answer to Double Line Problem #2:
For every handful of popcorn I grab to eat, I drop 2 kernels to the floor.  Every handful of popcorn has eight kernels in it. The bowl of popcorn gave me 9 handfuls.  How many kernels landed on the floor?  

This one is a little tough so bear with me.  Here's what we know:

• 2 kernels dropped per handful.
• 8 kernels per handful
• 9 handfuls total.

We need to find:  Quantity of kernels on the floor.

The "handful" makes it a little confusing, however, we are solving for the number of kernels on the floor, so we need to break everything down into kernels and forget the handful nonsense.

8 kernels per handful and 9 handfuls total means there are 72 kernels total (8 x 9 = 72).

The ratio is 2 kernels to 8 kernels (per handful), or 2:8.

Draw up the double lines and use the labels "Dropped" and "Handful".  Start labeling the "Handful" line with increments of 8 until you get to the total of 72.  I grabbed 9 handfuls of 8, so there are 9 vertical lines (not including the zero line).

On the "Dropped" line, label the vertical lines with increments of 2 starting from zero.

The answer is 18 kernels on the floor for the dog to eat.