How many slices could you image with a gradient-echo sequence which uses a 20 ms slice selection gradient, 10 ms phase encoding gradient, 100 ms frequency encoding gradient, and TR of 1 second?

For a gradient-echo sequence, the total sequence takes an amount of time equal to the sum of the slice selection gradient, phase encoding gradient, and frequency encoding gradient on times. In this case 130 ms. A total of seven 130 ms periods will fit into a 1 s TR peroid. [(1000 ms) / (130 ms) = 7.69 , but since we can not have fractions of a sequence the answer is 7.]