Question

What number should be added to each of the number 3,5,13and 19 so that the resulting number may be in proportion​

Answer 1

Answer:

Let the number be x

I suppose that the meaning of the question could be explained by this equation.

3+x5+x=13+x19+x

By doing criss-cross

(3+x)×(19+x)=(5+x)×(13+x)

57+22x+x2=65+18x+x2

Get the like terms together

22x−18x+x2−x2=65–57

Simplify

4x=8

x=2

Let's check our answer.

3+2=5 5+2=7 13+2=15 19+2=21

15/21 = 5/7

The answer is 2