Alarms from 3 different clocks sound after every 2, 4 and 6 hours, respectively. If the clocks are startedat the same 6 time, how many times do the alarms ring together in 3 days?
The weights of 4 boxes are 100, 70, 50 and 90 kilograms. Which of the following cannot be the total weight, in kilograms, of any combination of these boxes and in a combination a box can be used only once?