Problem: A bicycle wheel makes Revolution per minute to maintain a speed of 8.91 km per hour. Find the diameter of the wheel.

Solution:

Given:
- Speed of the bicycle = 8.91 km per hour
- Revolution per minute = Unknown
- Diameter of the bicycle wheel = Unknown

We need to find the diameter of the bicycle wheel. To do this, we need to use the following formula:

Circumference of the wheel = Distance covered in one revolution

We know that the distance covered by the bicycle in one minute is equal to the speed of the bicycle divided by the number of minutes in an hour (60). Therefore, the distance covered by the bicycle in one minute is:

Distance covered in one minute = 8.91/60 = 0.1485 km

We also know that the distance covered in one revolution is equal to the circumference of the wheel. Let the diameter of the wheel be d. Then, the circumference of the wheel is:

Circumference of the wheel = πd

Now, let's assume that the bicycle makes n revolutions per minute. Therefore, the distance covered in one minute is also equal to the distance covered in one revolution multiplied by n. Therefore, we have:

0.1485 = πd * n

Solving for d, we get:

d = 0.1485 / (πn)

Therefore, the diameter of the bicycle wheel is given by the formula:

d = 0.1485 / (πn)

where n is the number of revolutions per minute.

Therefore, to find the diameter of the bicycle wheel, we need to know the number of revolutions per minute.