Find the fourth proportional to the numbers 21, 33 and 56.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 88
The fourth proportional to \(a,\ b,\ c\) is the number \(d\) with \(a:b=c:d\), so \(\displaystyle d=\frac{b\times c}{a}\).
\(21:33=56:d\)
\(\displaystyle d=\frac{33\times56}{21}=\frac{1848}{21}=88\)
The fourth proportional is 88.