An oscilloscope is set on a TIME/DIV setting of 50 ms. There are 10 divisions on the time scale. A sinewave on the oscilloscope display has exactly three full cycles of the sine wave that fit on the 10 divisions. What is the frequency of the wave?
Since the TIME/DIV setting is set to 50 ms, and there 10 divisions on the time scale, that means that full scale display is 500 msec.
If a sinewave has exactly three full cycles of the sine wave that fit on the 10 div, this means that one cycle is just one-third of the 10 div value, as follows:
    [tex]T = \frac{500 msec}{3} = 166.7 msec (1)[/tex]
Since the frequency of a wave is just the number of cycles per unit time, can be written as follows:
