First Step [Math Class -Percent Problems]


We normally teach our students to set up a proportion as “part/whole = n/100” to help them solve problems with percent. There are some students, however, that don’t “see” how the proportion was set up and assume that “part” is always smaller than the “whole”. duck-2236908__340They prefer to use a “better” visual. First, students can use  a “drawing” that could take different shapes depending on their preference to make it easier for them to remember its parts. I was thinking about using silly names such as “The Upside Down Triangle”, “The Kite”, “The T-Bone Steak”, or “The Ice Cream Cone”.

Students can use one of your drawings or you can allow them to create their own. As long as they remember the three parts they can come up with a variety of ideas. It may seem time consuming at the beginning. I know my students love to draw. No matter the choice, the drawing has the same three parts for all three possible percent problems. Each part of the problem fits in one section. Setting up the proportion is always done in the same order. Students need to know that percent means “out of a hundred” and still use cross products to solve the equation afterwards. It is that “first step” of setting up the proportion correctly that sometimes they stumble upon. After a while, they will notice that there is a “T” shape inside each design and won’t have to use the full picture. I used one problem for each situation. Every little bit helps.

Problem# 1: What percent of 50 is 14.5?

20170508_224620-1Step 1: Write the equation X/100 = 14.5/50

Step 2: Solve the equation 50 × X = 14.5 × 100

50 × X = 145 (divide both sides by 50)

X = 2.9

Step 3: Check solution 50 × 2.9 = 14.5 × 100

145 = 145 

Problem# 2: 32% of what number is 15.36?20170508_225950-1Step 1: Write the equation 32/100 = 15.36/X

Step 2: Solve the equation 32 × X = 15.36 × 100

32 × X = 1,536 (divide both sides by 32)

X = 48

Step 3: Check solution 32 × 48 = 15.36 × 100

1,536 = 1,536 

Problem# 3: What number is 15% of 115?20170508_231704-1Step 1: Write the equation 15/100 = X/115

Step 2: Solve the equation 15 × 115 = 100 × X or

100 × X = 15 × 115

100 × X = 1,725 (divide both sides by 100)

X =  17.25

Step 3: Check solution 15 × 115 = 100 × 17.25

1,725 = 1,725 

Featured Image and photo: http://www.pixabay.com

Also see [math technique] About Those Percentages…

 

 

 

 

 

 

 

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