Question 853745
"A father is nine times the age of his son. In 5 years, he will be 4 times the age of his son. How old are they now?


x = age of son now
y = age of father now


y=5x for "now".
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Their ages five years from now are these:
x+5 = age of son in five more years
y+5 = age of father in five more years
y+5=4(x+5) ---- He will be four times the age of his son.


SUMMARY OF EQUATIONS:
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y=5x
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y+5=4(x+5)
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SOLVING THE SIMULTANEOUS EQUATIONS
y+5=4x+20 from the 'in five years' equation;
4x+20=y+5
4x-y=5-20
y-4x=15
Substitute y using the 'now' equation;
5x-4x=15
1*x=15
x=15--------------part of the answer.  The son, now.
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Now compute y.
y=5x
y=5*15
y=75-------------other part of answer.  The father, now.