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All courses Math Foundations · MF.PR.4 18 of 60
Use ratio tables and double number lines to solve missing-value and scaling problems.

Complete a ratio table entry

Problem
Use the ratio table to find the missing value.

Apples | Dollars
3 | 2
12 | What number goes in the blank?
Ratio table with columns Apples and Dollars. The first row shows 3 apples and 2 dollars. The second row shows 12 apples and a blank dollar value. Open full size
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Hint

Look at the apples column first: how do you get from 3 apples to 12 apples?

In a ratio table, both entries in a row must scale by the same multiplicative factor to keep the ratio equivalent.

Solution walkthrough

01

Use the known ratio

\[3~\text{apples}~=~2~\text{dollars}\]

Each row in the ratio table must match this same apples-to-dollars relationship.

02

Find how the apples changed

\[3~\to~12~=~\times~4\]

The number of apples went from 3 to 12, so the apples were multiplied by 4.

03

Scale the dollars the same way

\[2~\times~4~=~8\]

To keep the ratio equivalent, the dollars must be multiplied by the same factor, 4.

04

State the missing value

\[12~\text{apples}~=~8~\text{dollars}\]

The number that goes in the blank is 8.

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Another way

  1. Find the cost of 1 apple first: $2 ÷ 3 = 2⁄3$ dollar per apple. Then for 12 apples, $12 × 2⁄3 = 8$ dollars.

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Common mistake

Adding instead of scaling. For example, going from 3 apples to 12 apples is not +9 dollars. The table must keep the same multiplicative ratio, so since 3 became 12 by multiplying by 4, 2 must also become 8 by multiplying by 4.