Bill, Phil and Jenny are siblings. Bill is twice as old as Phil. Jenny is two years younger than Bill. Currently, their dad is twice as old as the sun of their ages. In nine years, their dad's age will be equal to the sum of his three kids' ages at that time. What is Jenny's
current age?

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  6

Step-by-step explanation:

Let p, b, j, d represent the ages of Phil, Bill, Jenny, and Dad. We are given the relations ...

  b = 2p

  j = b -2

  2(p +b +j) = d

  (p+9) +(b+9) +(j+9) = d+9

Solving the last equation for d, we get ...

  (p +b +j) +18 = d

Substituting for the sum of p, b, j in the third equation, we have ...

  2(d -18) = d

  d = 36 . . . . . . . . add 36-d

Substituting for b and j in the third equation, we get ...

  2(p +(2p) +(2p-2)) = 36 . . . . .  uses b=2p in the 2nd equation

  10p -4 = 36 . . . . . . . . . . . . . . . collect terms

  p = 40/10 = 4 . . . . . . add 4; divide by 10

  b = 2p = 8

  j = b -2 = 6

Jenny's current age is 6.

All of the ages are ...

  Bill: 8; Jenny: 6; Phil: 4; Dad: 36

step-by-step explanation:

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