Big Ideas Math: Modeling Real Life, Grade 7
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Big Ideas Math: Modeling Real Life, Grade 7 View details
4. Writing and Solving Proportions
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Exercise 9 Page 205

Solve for the variable by using the Cross Products Property.

z = 15

Practice makes perfect
To solve the proportion, we will start by using the Cross Products Property. Remember that we will need to treat z+1 as a single quantity in the cross multiplication process.
40/z+1 = 15/6
40 * 6 = (z+1) * 15
240 = (z+1) * 15
From here, we will continue solving for x by using the Distributive Property and the Properties of Equality.
240 = (z+1) * 15
240 = 15z + 15
240-15 = 15z + 15-15
225 = 15z
225/15 = 15z/15
15 = z
z = 15