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How can I use a ratio table to find equivalent pairs?

Quick answer

Put the two quantities in separate columns, then multiply or divide both entries in a pair by the same factor. For example, starting with 2 red counters for every 3 blue counters, multiplying both numbers by 2 gives 4:6; multiplying both by 3 gives 6:9. The pairs are equivalent because their ratios remain equal. A table makes the matching pairs and their pattern easy to see.

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Question

I have a ratio of 2 red counters to 3 blue counters. How do I start a ratio table to find equivalent pairs?

Geez

Make one column for each quantity and put the starting pair together in the first row. Keep the order consistent: red counters first, blue counters second. Then choose a scale factor and apply it to both numbers. Equal ratios have the same quotient; multiplying both parts of a ratio by the same factor keeps that relationship unchanged. [S1]

For example, multiply both 2 and 3 by 2 to get 4 and 6. The table organizes those paired values; the important part is keeping the same multiplier for both entries.

Follow-up question

Can you show a completed table and explain how the pattern appears?

Geez

Here is a small table using whole-number scale factors:

Scale factor | Red counters | Blue counters
1            | 2            | 3
2            | 4            | 6
3            | 6            | 9
4            | 8            | 12

Each row comes from the original pair, 2:3. For instance, the row with factor 3 comes from 2 × 3 = 6 red counters and 3 × 3 = 9 blue counters, so it gives 6:9. The pattern is that each step here adds 2 red counters and 3 blue counters. That pattern is visible in this table; the reliable check is that both entries in each row use the same scale factor as the starting pair. [S1]

Follow-up question

What if I know one value in a pair and need to find the other? How do I avoid using the wrong factor?

Geez

Compare the known value with the corresponding value in the starting pair, not with the other column. If the red-counter value changes from 2 to 10, the factor is 10 ÷ 2 = 5. Apply that factor to the blue-counter value too: 3 × 5 = 15. So the matching pair is 10 red counters to 15 blue counters.

A common slip is to add the same amount to both entries instead. Adding 2 to 2:3 gives 4:5, which does not use one shared multiplier. Check your result by comparing the ratios: 10:15 has the same quotient as 2:3. [S1]

Follow-up question

Could you give me a quick routine I can reuse on a different ratio?

Geez

Use this routine:

  1. Write the starting pair in a consistent order, such as apples then oranges.
  2. Choose a scale factor, or work out the factor from the known value and its matching starting value.
  3. Multiply or divide both starting values by that same factor.
  4. Put the resulting values in the same row and label the quantities.
  5. Check that the pair still represents the same ratio.

For example, if a new starting pair is 4 apples to 5 oranges and you choose factor 3, the row is 12 apples to 15 oranges. Keep the labels and order clear so you do not accidentally match a value from one column with the wrong starting value.

A practical checklist

  • Label both quantities and keep their order consistent.

  • Write the original pair together in the first row.

  • Use one shared scale factor for both entries in every new pair.

  • If one value is known, compare it with the matching starting value to find the factor.

  • Check that the resulting ratio is equivalent to the original.

A few more useful answers

Can I use a scale factor smaller than 1?

Yes. For example, dividing both entries by the same number scales both together. The resulting values may be fractions or decimals, depending on the starting pair and factor.

Why can’t I add the same number to both parts of a ratio?

Adding the same amount does not generally preserve the ratio. Equivalent pairs come from applying the same multiplier or divisor to both entries.

Does every row have to use a whole-number scale factor?

No. Whole-number factors make the example easy to read, but the key is using the same factor for both quantities. Whether the resulting values are convenient depends on the ratio and factor you choose.

Sources

References used for this guide.

  1. [S1] OpenStax Contemporary Mathematics: Ratios and Proportions
    openstax.org · Checked

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