A researcher is comparing average home values in four California cities. She assigns one her four research assistants to each of the cities. The fourth assistant notes that his city is composed of 30% low income areas, 50% middl income areas, and 20% high income areas. He therefore randomly selects 15 houses from the low income areas, 25 houses from the middle income areas, and 10 houses from the high income areas. This is an example of what type of sampling?

A man can drive a motorboat 64 miles down the Colorado River in the same amount of time that he can drive 16 miles upstream. Find the speed of the current if the speed of the boat is 10 mph in still water.

this is incorrect and due at 5:00 please help