P is directly proportional to Q and Q = 7 when P = 15. Find P when Q = 14.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 30
When P is directly proportional to Q, \(P=kQ\) for a fixed constant \(k\): P changes in the same ratio as Q.
From P = 15 when Q = 7: \(15=k\times7\), so \(k=\displaystyle\frac{15}{7}\)
When \(Q=14\): \(P=\displaystyle\frac{15}{7}\times14=30\)
Seen another way, Q has doubled from 7 to 14, so P doubles from 15 to 30.