## Elementary Algebra

$3$
We let the unknown number be $x$. Two times the unknown number is $2x$ while one more than two times the unknown number is $(2x+1)$. Four times the unknown number is $4x$. The question states that one more than two times a certain number is five less than four times the number. This means that $2x+1$ is equal to $4x-5$. Therefore, we write the following equation and solve: $2x+1=4x-5$ $4x-(2x+1)=5$ $4x-2x-1=5$ $2x-1=5$ $2x=5+1$ $2x=6$ $x=3$ Therefore, the unknown number is $3$.