From the condition, - the probability that tube light A is working at a given day is 1 - 0.2 = 0.8, and - the probability that tube light B is working at a given day is 1 - 0.15 = 0.85. Therefore, the probability that both tube lights are working at a given day is the product 0.8*0.85 = 0.68. ANSWER It is the exact / precise value, so rounding is not required.