the speed of a railway engine is 63 km per hour when no compartment is attached , and the reduction in speed is directly proportional to the square root of the number of compartments attached . if the speed of the train carried by this engine is 24 km per hour when 9 compartments are attached , the maximum number of compartments that can be carried by the engine is :
the reduction in speed is directly proportional to the square root of the number of compartments attached does reduction mean amount subtracted ? or percentage decrease ? there are at least two interpretations , and the wording does not provide a clear interpretation between them . evidently what the question intends is the subtraction interpretation . what is subtracted from the speed is directly proportional to the square root of the number of compartments attached . in other words , if s = speed , and n = number of compartments , then s = 63 - k * sqrt ( n ) where k is a constant of the proportionality . in general , if a is directly proportional to b , we can write a = k * b and solve for k . if n = 9 , then s = 24 24 = 63 - k * sqrt ( 9 ) = 63 - 3 k k = 13 now , we need to know : what value of n makes s go to zero ? 0 = 63 - 13 * sqrt ( n ) 13 * sqrt ( n ) = 63 n = 23 with 24 compartments , the train does not budge . therefore , it would budge if there were one fewer cars . thus , 23 is the maximum number of cars the engine can pull and still move . e
power(divide(63, divide(subtract(63, 24), sqrt(9))), const_2)