tom drives from town r to town b , driving at a constant speed of 60 miles per hour . from town b tom immediately continues to town c . the distance between r and b is twice the distance between b and c . if the average speed of the whole journey was 36 mph , then what is tom ' s speed driving from b to c in miles per hour ?
let ' s assume that it takes 4 hours to go from point r to b . then the distance between them becomes 240 which makes distance between b and c 120 . ( 240 + 120 ) / ( 4 + x ) gives us the average speed which is 36 . you find x = 6 . so the question simplifies itself to 120 / 6 = 20 hence the answer is b .
divide(const_1, subtract(divide(add(const_1, const_2), 36), divide(const_2, 60)))