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
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.