Page 76 - BUSINESS MATHEMATICS MODULE 1 (WHOLE)_revised 10.20.2020

LESSON 5.B: RATIOS AND PROPORTIONS

• How to find an unknown term in a proportion.

Let us start with the terms we have been using, i.e. 2 ∙ 10 = 5 ∙ 4. Assuming that
the first term is unknown, and the rest are known, we have,

1. Let the first term
× 10 = 5 × 4
10 = 20
10 20
=
10 10
= 2
As we can see, 2 is our first term.

2. If the fourth term is unknown
Let the fourth term

2 ∙ 10 = 5 ∙
20 = 5N
20 5
=
5 5
4 =
As we can see, 4 is our fourth term

• Word Problems
We can express the concept of proportions in word problems. The following examples

will illustrate this point.

Example 1: If 6 Mathematics notebooks cost ₱43.50, how would 2 notebooks of the

same type cost?

Solution:
Rule: The product of the means = the product of the extremes.

Thus, 6 ∶ ₱43.50 = 2 ∶ Check:
6 = 43.50(2) 6 = ₱87.00
6 87 6(₱14.50) = ₱87.00
=
6 6 ₱87.00 = ₱87.00
= ₱14.50

Example 2. How much would 3 pens cost if 7 pens can be bought for ₱9.10?

Solution: 3: = 7: 9.10 Check:
7 = ₱27.30 7 = ₱27.30
₱27.30
= 7(₱3.90) = ₱27.30
7 ₱27.30 = ₱27.30
= ₱3.90

Page | 5.6 BUSINESS MATHEMATICS: MODULE 1