Question 241577
John is now 4 times as old as his brother Sam, so...
Let Sam = x
Let John = 4x
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In 4 years, John will be twice as old as Sam will be then.  Our equation now becomes: John in 4 years = twice Sam in 4 years
{{{4x+4=2(x+4)}}}
Now solve for x to determine Sam's age.
{{{4x+4=2x+(2*4)}}}
{{{4x+4=2x+8}}}
{{{4x-2x=8-4}}}
{{{2x=4}}}
{{{x=2}}} ...this is Sam's age (today)
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{{{4x=4*2=8}}} ...this is John's age (today)
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Now let's plug the x value in the original equation to see if it makes sense.
Remember: {{{4x+4=2(x+4)}}}
{{{4(2)+4=2(2+4)}}}
{{{8+4=(2*2)+(2*4)}}}
{{{12=4+8}}}
{{{12=12}}} ...the x value checks! 
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Done!