If 5 students utilize 18 pencils in 9 days, how long, at the same rate, will 66 pencils last for 15 students?
Answer
No answer key was printed for this question.
Explanation
Let the required number of days be $x$. More students, Less days (Indirect Proportion). More pencils, More days (Direct Proportion). Students $15:5$, Pencils $18:66$, $::9:x$. $\therefore (15\times18\times x)=(5\times66\times9) \Leftrightarrow x=\left(\frac{5\times66\times9}{15\times18}\right)=11$. Hence, the required number of days is 11.
Explanation as extracted from the printed page; notation may be imperfect.