Consider the data of a certain number of activities of type P, Q, and R in the percentage of the total activities of the cities B, C, D, and K in the table below.

Activity \ City	B	C	D	K
P	45	30	25	35
Q	25	30	35	30
R	30	40	40	35

If the total activities of B and C are 500 and 400, respectively, then what is the difference in activity R of B and C?

The correct answer is 10.

To find the difference in activity R for cities B and C, we can follow these steps:

Step 1: Extract the percentage values from the table.
According to the given table:
- The percentage of activity R in city B is 30% of the total activities of B.
- The percentage of activity R in city C is 40% of the total activities of C.

Step 2: Calculate the number of activities of type R in city B.
The total activities for city B are given as 500.

$\text{Activity R in B}=30\%\text{ of }500$

$\text{Activity R in B}=\frac{30}{100}\times 500=150$

Step 3: Calculate the number of activities of type R in city C.
The total activities for city C are given as 400.

$\text{Activity R in C}=40\%\text{ of }400$

$\text{Activity R in C}=\frac{40}{100}\times 400=160$

Step 4: Find the difference between the two values.

$\text{Difference}=\text{Activity R in C}-\text{Activity R in B}$

$\text{Difference}=160-150=10$

Therefore, the difference in activity R of B and C is 10.