Let's first calculate the probability that the string of lights WILL work. Then we'll subtract that from 1 to find the probability that it will FAIL to work. For the string of lights to WORK, that means: the 1st bulb works AND the 2nd bulb works AND the 3rd bulb works AND ∙∙∙ the 24th bulb works. So that's (0.97)(0.97)∙∙∙(0.97) to 24 factors or (0.97)24 = 0.4814172219 or a string will work about 48% of the time. So the other 52% of the time a string will fail. We calculate 1 - 0.4814172219 and get 0.5185827781 or a probability of 51.85827781% of the time that a string will fail, and then round that off to as many decimal places as your teacher says to round it. Edwin