What is the number?

Question

20% of a number is x. The number is 4 more than x.

Answer 1

Let....

 

y=unknown number

x=0.2y.............Eq1, given, problem statement

y=x+4.............Eq2, given, problem statement

 

0.2y=x.............Eq1, solve for "y" in terms of "x"

     y=1/(0.2x)...divide both sides by 0.2

     y=5x...........simplify, now have "y" in terms of "x"

 

5x=x+4............Eq2, substitute above for "y"

4x=4................subtract "x," both sides

  x=1

 

0.2y=1.............Eq1, substitute for "x"

     y=1/(0.2)....divide both sides by 0.2

     y=5

 

So "x=1, y=5".  Let's check our solution.  Plug these values back

into the original Eq1, Eq2...

 

1=0.2(5)..........Eq1, substitute values

1=1.................true, √check

 

5=1+4.............Eq2, substitute values

5=5.................true, √check

 

Always check your work, solutions.