If Owawa makes 7200 revolution in 5 hours, how many revolution does it make per minute?

Total revolutions = 7200
Total time = 5 hours

There are 60 minutes in 1 hour.

Owawa makes 24 revolutions per minute.

The correct option is (b).

Total number of students = 30
Average score of 30 students = 6
Total score = Average score $\times$ Number of students

Sum of scores for 28 students = 160

Number of remaining students = $30 - 28 = 2$
Sum of scores for remaining 2 students = Total score - Sum of scores for 28 students

Average mark = $\frac{\text{Sum of scores for remaining 2 students}}{\text{Number of remaining students}}$

The average mark of the two remaining students is 10.

The correct option is (d).

Principal (P) = N280
Rate (R) = 3% per annum = $\frac{3}{100} = 0.03$
Time (T) = $2\frac{1}{2}$ years = 2.5 years

The simple interest is N21.

Amount = Principal + Simple Interest
Amount = N280 + N21 = N301
The total amount after $2\frac{1}{2}$ years is N301.

The correct option is (d).

The phrase "increase of N240 by ratio 3:5" means that the original amount (N240) corresponds to the first part of the ratio (3), and the new amount corresponds to the second part (5).
Let the original amount be $A_o = \text{N}240$.
Let the new amount be $A_n$.
The ratio of original to new is $3:5$.

The new amount after the increase is N400.

The actual increase is $400 - 240 = 160$. However, N160 is not an option, while N400 is an option. This suggests the question is asking for the new value after the increase, rather than the amount of the increase itself.

The correct option is (c).

The figure shows a right-angled trapezium.
The parallel sides are the top and bottom horizontal lines.
Length of the top parallel side ($a$) = 24 cm.
Length of the bottom parallel side ($b$) = $6 \text{ cm} + 24 \text{ cm} = 30 \text{ cm}$.
The height ($h$) is the perpendicular distance between the parallel sides, which is the vertical line on the right = 10 cm.

The area of the trapezium is $270 \text{ cm}^2$.

The correct option is (c).