Question

When fifteen is reduced by one third of a number, the results is 7. The number

Answer 1

we wirte the expression on numbers

$15-\frac{x}{3}=7$

where x is the missing number

to solve

subtract 15 on both sides

$\begin{gathered} 15-15-\frac{x}{3}=7-15 \\ -\frac{x}{3}=-8 \end{gathered}$

we can remove negative sign on both sides

$\begin{gathered} \frac{x}{3}=8 \\ \end{gathered}$

and solve for x multipliying 3 on both sides

$\begin{gathered} 3\times\frac{x}{3}=8\times3 \\ \\ x=24 \end{gathered}$

the value of missing number is 24

Other way

$15-\frac{x}{2}=7$

solve for x moving terms

$\begin{gathered} -\frac{x}{3}=7-15 \\ \\ -\frac{x}{3}=-8 \\ \\ x=-8\times-3 \\ \\ x=24 \end{gathered}$