What percentage of families in the city have telephones? I. 50% of the families of the city possess television. II. 30% of the television owners of the city have telephones.
Answer
SELF-PRACTICE — the source book printed no answer.
Nothing is invented here, so this question has no answer on record.
Explanation
Let the total number of families be $x$. Then, from I and II, we have Number of families which have telephones $$\begin{aligned} & =30 \% \text { of } 50 \% \text { of } x=\left(\frac{30}{100} \times \frac{50}{100} \times x\right) \\ & =\frac{15}{100} x=15 \% \text { of } x . \end{aligned}$$ ∴ Required percentage $=15\%$. So, both I and II are required to answer the question. $$\therefore \quad \text { Correct answer is }(e) \text {. }$$
Explanation as extracted from the printed page; notation may be imperfect.