The true distance P must be 45 as the retracement distance 84 is to 80.

So, we put it into a simple formula. P1 is to 45 as 84 is to 80, or P1 divided by 45 equals 84 divided by 80. To get our knowns on one side, we shift the 45 over so P1 equals 45 times 84 divided by 80. Using our calculator, this quickly figures out to be 47.25 which is the right amount longer than 45. It is proportionally greater by the same amount that 84 is greater than 80. That applies to calculating P2 also.

If you would like to check this problem for additional practice, use the Proportion Calculator to compute the numbers.

We have just calculated a simple problem in single proportionate measurement often called two-way proportion. It is applied in any situation where we must keep our unknown point on the true line between two known points. It can also determine the placement of more than one point on such a line.

Next, it's your turn to try.