
David L. answered 09/16/19
Ph.D. Chemist tutoring math and science
As the problem states, let x = the current age of the youngest sister. Since the ages of the sisters are consecutive even integers, the age of the middle sister is x+2 and the age of the oldest sister is x+4. The problem states that the product of the ages of the youngest and oldest sister, x*(x+4) is 20 more than twice the middle sister's age. The equation is therefore
x*(x+4) = 2(x+2) +20
Simplify to get x^2 +4x = 2x + 24
Rearrange to get
x^2 + 2x -24 = 0
Factor to get (x+6)*(x-4) = 0. Therefore, either x+6 = 0, in which case x = -6, or
x-4 =0, in which case x=4. Since x is an age, reject the negative value. Therefore, the age of the youngest sister is 4, and her other sisters are 6 and 8 years old, respectively.
In seven years the sisters will be 11, 13 and 15 years old. The sum of these ages is 39.