1956 AHSME Problems/Problem 47

In 1 day, $x$ machines can do $\frac {1}{3}$ of the job , and $x + 3$ machines $\frac {1}{2}$ of the job. So $3$ machines can do $\frac {1}{2} -\frac {1}{3}=\frac {1}{6}$ of the job in 1 day, and 1 machine can do $\frac {1}{18}$ of the job in 1 day. Hence, **18** days are needed for 1 machine to complete the job;