working alone , a can complete a certain kind of job in 15 hours . a and d , working together at their respective rates , can complete one of these jobs in 10 hours . in how many hours can d , working alone , complete one of these jobs ?
"let total time taken by d to complete the job = d total time taken by a to complete the job = 15 work done by a in an hour 1 / a = 1 / 15 working together a and d can complete the job in 10 hours 1 / a + 1 / d = 1 / 10 = > 1 / d = 1 / 10 - 1 / 15 = 1 / 10 - 1 / 15 = 1 / 30 = > d = 30 hours answer e"
inverse(subtract(inverse(10), inverse(15)))