Question

what number must be added to each of the number 18 20 21 24 to get the number which are in proportion

Answer 1

But they r in which proportion

Mention that also in the q

Answer 2

Call the one value to be added by some name; say, “x”. Then we need x to create a true proportional statement; namely:

5+x9+x=13+x21+x

5+x9+x=13+x21+x

Cross-Multiply to get a quadratic equation:

105+26x+x2=117+22x+x2

105+26x+x2=117+22x+x2

Subtract the identical squared term from either side. Then solve the resulting linear equation for the value that must be added.