sanju09 wrote:A wheel of radius 2 meters is turning at a constant speed. How many revolutions does it make in time T?

1. T = 20 minutes.
2. The speed at which a point on the circumference of the wheel is moving is 3 meters per minute.

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Asking about the number of revolutions the wheel makes is equivalent to asking about what distance the wheel could spin over. Since we have radius, we can determine circumference. But distance = rate multiplied by time. Statement 1 is insufficient because you need to know how fast the wheel is turning in order to determine the number of revolutions it makes. Statement 2 is also insufficient, because you need to know what T equals. Taken together, you have rate and time, which allows you to determine distance, and you can use that with the wheel's circumference to determine the number of revolutions.