Answer:
Mark is 9.
Explanation:
We can use algebra or basic arithmetic to solve this.
Algebra:
(x+5)+x=23
In this case, x is the age of mark. (x+5) is the age of his brother, since Mark's brother is 5 years older than him.
x+x+5=23
subtract the 5 from both sides of the equation.
x+x=18
add the two x on the left side
2x=18
now divide both sides by 2
x=9. Therefore, Mark is 9.
Arithmetic:
23-5
We remove how how many years older Mark's brother is than him. Since Mark's brother is 5 years older, remove that from the total sum.
18
18 is Mark's age and his brother's without the 5 years, so cut it in half now.
9. Mark is 9.