5% of p is 10, and 10% of q is 5. r is equal to q/p. What is the value of r?

Correct option is B

Given
​$$5\% \ of \ p = 10\\\ \\10\% \ of\ q = 5r = \frac{q}{p}$$​​

Solution
Step 1: Find p
\frac{5}{100} \times p = 10
p = \frac{10 \times 100}{5} = 200

Step 2: Find q
​$$\frac{10}{100} \times q = 5\\\ \\q = \frac{5 \times 100}{10} = 50$$​​

Step 3: Find r 

​$$r = \frac{q}{p} = \frac{50}{200} = \frac{1}{4}$$​​

Final Answer
So the correct answer is (b)