Summary of equations

Question

The total of Mark and Johns age is 74. Mark is one less than double John's age. How old are these two individuals?

Answer 1

Hi Joscef:

From the information given we can set up 2 equations

forming a system to solve:

 

The total of Mark and John's age is 74:

m + j = 74    {equation 1}

 

Mark is one less than double John's age:

m = 2j - 1     {equation 2}

 

Since we know that m = 2j-1 from the 2nd equation,

solve by substitution.  Substitute 2j-1 in place of m in

1st equation to solve for j.

 

2j -1 + j = 74

3j - 1 = 74

3j = 75

j = 25

 

John is 25 years old.

m = 2j - 1 = 2(25)-1 = 49 years old for Mark.

 

Questions?