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Ana is 5 years older than Beth. In 5 years, the product of their ages is 1.5 times the product of their present ages. How old is Beth now?

Sagot :

Let x be Beth's age, since Ana is 5 years older, then
      x+5 would be Ana's age.

In five (5) years, Beth's age will be 5+x and Ana's age will be 5+(x+5). So,
Beth after 5 years = x+5
Ana after 5 years = x+10

The product of their ages 5 years after is 1.5 times the product of their present ages. Thus,
[tex](x+10)(x+5)=1.5x(x+5)[/tex]
[tex] x^{2} +15x+50=1.5 x^{2} +7.5x[/tex]
[tex] x^{2} -1.5 x^{2} +7.5x+50=0[/tex]
([tex]-0.5 x^{2} +7.5x+50=0[/tex] )(-2)        (Multiply both sides by -2)
[tex] x^{2} -15x-100=0[/tex]                    (Factoring)
[tex](x-20)(x+5)=0[/tex]
x=20; x=-5                           (x=-5 is rejected since we have no negative age)

So, the age of Beth now is 20; furthermore, Ana's age (x+5=20+5=25) is 25..