each light bulb at a hotel is either incandescent or fluorescent . at a certain moment , thirty percent of the incandescent bulbs are switched on , and eighty percent of the fluorescent bulbs are switched on . if 70 percent of all the bulbs are switched on at this moment , what percent of the bulbs that are switched on are incandescent ?
let i be the number of incandescent bulbs . let f be the number of fluorescent bulbs . 0.3 i + 0.8 f = 0.7 ( i + f ) 0.1 f = 0.4 i f = 4 i this means that for every 1 incandescent bulb , there are 4 fluorescent bulbs . the percent of bulbs that are switched on which are incandescent is : 0.3 i / ( 0.3 i + 0.8 f ) = 0.3 i / ( 0.3 i + 0.8 * 4 i ) = 0.3 i / 3.5 i = 3 / 35 which is about 8.6 % . the answer is b .
multiply(divide(multiply(subtract(multiply(divide(divide(subtract(multiply(multiply(const_4, const_2), multiply(add(const_4, const_1), const_2)), 70), subtract(70, multiply(const_3, multiply(add(const_4, const_1), const_2)))), add(const_4, const_1)), multiply(add(const_4, const_1), const_2)), divide(multiply(const_3, multiply(add(const_4, const_1), const_2)), const_100)), multiply(const_3, multiply(add(const_4, const_1), const_2))), 70), const_100)