Use Proportions Math Skills LESSON 1

Name
Date
Class
Math Skills
LESSON 1
Use Proportions
A proportion is an equation that shows that two ratios are equal. When two ratios form
a proportion, the cross products are equal. In this example, the cross products are 2 × 10
and 4 × 5.
5
2 = ___
If __
, then 2 × 10 = 4 × 5.
10
4
If one of the numbers in a proportion is unknown, cross multiply to change the proportion
to an equation. Then solve the equation for the unknown number.
You know that 1 cell produces 2 daughter cells at the end of mitosis. How many daughter
cells will be produced by 19 cells?
Step 1 Use the information in the problem to write a proportion.
1
__
2
19
= ___
n
Step 2 Cross multiply to solve for the unknown number.
1 × n = 2 × 19
n = 38
Step 3 Use the solution to answer the question in the original problem situation.
The 19 cells will produce 38 daughter cells.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Practice
1. If 7 cells go through mitosis, how
many daughter cells will be produced?
3. The egg of a type of frog is 1.5 mm
wide. If you place 12 eggs in a line,
what is the length of the line from end
to end?
Reproduction of Organisms
2. If 47 sex cells go through meiosis, how
many daughter cells will be produced?
4. For another type of frog, 3 eggs in a
row measure 6 mm across. What is the
length of a line of 12 eggs?
17