Big Ideas Math: Modeling Real Life, Grade 6
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Big Ideas Math: Modeling Real Life, Grade 6 View details
1. Ratios
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Exercise 49 Page 114

Define variables for the side lengths.

Perimeter: 67.5 inches
Explanation: See solution.

Practice makes perfect

Consider that the ratio of the side lengths of a triangle is 2:3:4. We want to find the perimeter of the triangle if the shortest side is 15 inches. To do so, let's start by define the side lengths.

  • x as the shortest side.
  • y as the longest side.
  • z as the middle side.
This means that the ratio x:y is equal to ratio of the shortest and longest side, 2:4. The same will occur with the value of the ratios. x/y=2/4In our case, the shortest side is x= 15. Let's substitute this value into the equation and solve for y.
x/y=2/4
â–Ľ
Solve for y
15/y=2/4
15/y* y=2/4* y
15=2/4* y
15=2y/4
15 * 4=2y/4 * 4
15 * 4 =2y
60=2y
60/2=2y/2
60/2=2y/2
30=y
y=30
This means that the longest side in the triangle is 30 inches long. Now we can use a similar procedure for the third side. This time the ratio z:y will be equal to the ratio of the middle side and the longest side. z/y=3/4 The longest side of the triangle is y= 30. Let's substitute this value into the equation and solve for z.
z/y=3/4
â–Ľ
Solve for z
z/30=3/4
z/30* 30=3/4* 30
z=3/4* 30
z=3* 30/4
z=90/4
z= 22.5
The middle side is 22.5 inches long. Finally, let's calculate the perimeter by adding the three side lengths. P=15+30+22.5 → P=67.5 The perimeter of the triangle is 67.5 inches.