Ratio of first number to second number = 3 : 5 and ratio of the second number to the third number = 4 : 7 Multiplying first equation by 4 and second equation by 5 to make the second (common) term equal. Let first number be = 2x , second number = 20x and third number = 35x ⇒ Sum = 12x+20x+35x=67x=67 ⇒ x=