Li needs 15 pieces of string each 1/2 of a inch long . She cut a 6 inch piece of string into pieces that are each 1/2 of an incch long . How many more pieces of string does she need?

If the speed of an electromagnetic wave is 100,000 cm/s and its wavelength is 100 cm, what is its frequency? a) 100,000 cycles per second (hz) b) 1 × 10-3 cycles per second (hz) c) 10,000,000 cycles per second (hz) d) 1,000 cycles per second (hz)