Question

If 3, 6, 12 and b are in continued proportion, then what is the value of b?

• A. b = 2
• B. b = 24
• C. b = 4
• D. b = 12

Answer 1

Answer:

B. b = 24

In a continued proportion:

$a : b = b : c = c : d$

So for (3, 6, 12, b):

$3 : 6 = 6 : 12 = 12 : b$

First check:
$\frac{3}{6} = \frac{6}{12} = \frac{1}{2}$

So,
$\frac{12}{b} = \frac{1}{2}$

b = 24