Question 997240: Petra is four times as old as her daughter Phillipa. In eight years time she will be five times as old as Phillipa. How old are Phillipa and Petra.
Thanks heaps I don,t know how to go about this one.
Answer by Theo(13342)   (Show Source):
You can put this solution on YOUR website! let x = petra's age.
let y = phillipa's age.
petra is 4 times as old as her daughter phillipa.
x = 4 * y
in 8 years time petra will be 5 times as old as phillipa.
x + 8 = 5 * (y + 8)
simplify to get x + 8 = 5 * y + 40
since you know that x = 4 * y, you can replace x with 4 * y in this equation to get:
4 * y + 8 = 5 * y + 40
now that your equation is one unknown variable in one equation, you can solve for that variable.
subtract 4*y from both sides of this equation to get:
8 = y + 40
subtract 40 from both sides of this equation to get:
-32 = y
since x = 4 * y, this means that x = -128.
you do not have a feasible solution because x and y have to both be positive.
if your problem was the other way around, this could be solved.
suppose petra's age today is 5 * phillipa's age.
if petra's age is 5 time's phillipa's age, how old is petra and phillipa 8 years from now.
you would start with:
x = 5 * y
you would then get x + 8 = 4 * (y + 8)
since x = 5 * y, you would replace x with 5 * y to get:
5 * y + 8 = 4 * (y + 8)
you would simplify to get 5 * y + 8 = 4 * y + 32
you would subtract 4 * y from both sides of the equation and you would subtract 8 from both sides of the equation to get:
y = 24
since x = 5 * y, you would also get x = 120.
5 * 24 = 120.
in 8 years time, x would be 128.
in 8 years time, y would be 32.
4 * 32 = 128.
still not very reasonable because it's unlikely that petra would be 120, but at least you would get a positive answer.
there is something wrong with the problem that you are not getting solutions that make sense.
the process as i just showed you above is correct.
if you couldn't find the answer and you were using this process, then it's not you.
it's the problem.
it's just not reasonable.
you should at least know how to solve this type of peoblem, even if the answer is not reasonable, or simply can't be found.
the process is what you need to learn.
there is also the question of the problem not being reasonable unless you were expeced to say that there was no feasible solution.
if you said that, you would be correct based on the way the problem is shown.
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