Question Video: Finding the Third Proportional to Three Given Numbers Mathematics • 7th Grade

Find the third proportional to 3, 33, and 11.

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Video Transcript

Find the third proportional to three, 33, and 11.

If the ratio 𝑎 to 𝑏 is equal to the ratio 𝑐 to 𝑑, then 𝑐 is said to be the third proportional. In the same way, 𝑏 would be the second proportional, 𝑎 would be the first proportional, and 𝑑 would be the fourth proportional.

In our example, if we let 𝑥 be the third proportional, we can say that the ratio three to 33 is equal to the ratio 𝑥 to 11. To get from the second proportional, 33, to the fourth proportional, 11, we can divide by three as 33 divided by three is equal to 11.

As the two ratios are equal to each other, in order to calculate, 𝑥 we need to divide the first proportional by three. Three divided by three will give us the value of 𝑥. As three divided by three is equal to one, we can say that 𝑥 equals one. This means that the third proportional to three, 33, and 11 is one.