Lizzy: For every 100 additional people that board a spaceship, its speed is halved. If the speed of the spaceship with 200 people on board is 500km per hour, what is its speed in km/hr when there are 400 people on board?.
Me: Hmmm, let me think. I think this is the detailed solution:
For every addition of 100 people added the speed is halved so for the first 100 people added its speed is 1 / 2 * 500 km / hr = 250 km / hr. For another addition of 100 people its speed is also halved, 1 / 2 * 250 km / hr = 125 km / hr. So for the total of 200 additional people, its speed is 125 km / hr. Final answer: 125.