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Sanjeev is twice as old as his son.If after four years he will be four times as old as his son was 9 years ago ,how old is each now ??

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    Let's let J represent Sanjeev and x represent his son.

    If J is twice as old as S then the equation is 2x=J

    After four years, so J+4, he is four times as old as his son, so 4x, was 9 years ago, so x-9, if you combine all the parts of that statement you get the equation: 4(x-9)= J+4.

    So now you have two different equations:
    2x=J
    4(x-9)=J+4

    So now you just substitute. We know that J=2x from the first equation so substitute 2x in for J in the second equation and solve for x:

    4(x-9)=(2x)+4
    4x-36=2x+4
    2x-36=4
    2x=40
    x=20

    so now we know that the son is 20 years old. Then plug in 20 for x in the first equation to find Sanjeev's age:

    2(20)=J
    40=J

    So Sanjeev is 40

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