Question

The product of 4 and a number x is at least 21

Answer 1

`the\ product\ of\ 4\ an\ number\ x\to4\cdot x=4x\\\\4x \ \textless \ 21\ \ \ \ |divide\ both\ sides\ by\ 4\\\\x \ \textless \ (21)/(4)\to x \ \textless \ (20+1)/(4)\to x \ \textless \ (20)/(4)+(1)/(4)\to x \ \textless \ 5+(1)/(4)\\\\\huge\boxed{x \ \textless \ 5(1)/(4)\to x\in\left(-\infty;\ 5(1)/(4)\right)}`