Which statement is true?
a) all waves travel at the same speed through any medium.
b) all waves travel at the same speed if no medium is present.
c) electromagnetic waves require a medium, but mechanical waves do not.
d) mechanical waves require a medium, but electromagnetic waves do not.

Solve for x -2.3(r - 1.2 ) = -9.66 enter you answer as decimal.

Acar started driving from city a to city b, distance between which is 620 miles, at a rate of 60 mph. two hours later a truck left city b and started moving towards city a at a rate of 40 mph. how many hours after the truck's departure will the two meet?

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?