Differential equations:
salt water pours into a full 20 litre tank at a rate of 2 l/min . the inflow initial concentration is 2 kg/l but after 30 minutes the inflow concentration switches to 1 kg/l . the brine in the tank is well mixed and it drains out at a rate of 2 l/min . call y the grams of salt in the tank at time t. the tank is initially full of fresh water. solve the differential equation that models the salt in the tank.
bonus: what is the maximum kg of salt ever in the tank?

Average acceleration: i have no idea how to do this.

Isuck at math ; ^; m a student solved this problem and said the answer is 3 feet. chase had a roll of ribbon that contained 7 7/8  feet of ribbon. he cut off one piece that was 3 5/8  feet long and another piece that was 1 1/4  feet from the roll. how much ribbon was left on the roll? is the student's answer reasonable? yes, the answer is reasonable. no, the answer is not reasonable. it should be about 2 feet. no, the answer is not reasonable. it should be about 13 feet. no, the answer is not reasonable. it should be about 4 feet.

How do i solve uniform motion problems?