A government study is undertaken with the aim of determining the benefits of a new driver training scheme and whether it has a different outcome on over-25 years old learner drivers than for under-25 years old learner drivers. The training program is undertaken for a group of 80 learner drivers, half of which are under 25 years old, half are over 25 years old. Then within each group of 40, half are randomly selected to participate in the new training program. The results are recorded and compared. This scenario is best described as an example of:

Aspacecraft can attain a stable orbit 300 kilometers above earth if it reaches a velocity of 7.7 kilometers per second. the formula for a rocket's maximum velocity v in kilometers per second is vequalsminus0.0098tplusc ln upper r, where t is the firing time in seconds, c is the velocity of the exhaust in kilometers per second, and r is the ratio of the mass of the rocket filled with fuel to the mass of the rocket without fuel. find the velocity of a spacecraft whose booster rocket has a mass ratio of 20, an exhaust velocity of 2.1 km/s, and a firing time of 15 s. can the spacecraft achieve a stable orbit 300 km above earth?