50 !
the pump used to fill the water tank on a fire truck takes 40 minutes to fill the tank. if the pump sending water to the hose is on, it takes 60 minutes to fill the tank. if the pump filling the water tank is off, how long does the pump sending water to the hose take to empty the tank?
a)120 minutes
b)60 minutes
c)30 minutes
d)24 minutes

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.