Answer:
D
Step-by-step explanation:
Just help a friend
We are trying to find the average speed of the plane, which is mph, or
. Using proportions, we can find the average speed of the plane in mph:

- Use the information from the problem to create a proportion. Remember that we are looking for mph, so we will call that
.

- Multiply the entire equation by


- Divide both sides of the equation by
to clear both sides of the mile unit
The average speed of the plane is 300 mph.
Answer:
40/9
Step-by-step explanation:
Use the work formula,
+
=
, where A is the amount of time it takes one person, B is the amount of time it takes another person, and T is the time it takes for them to work together.
Plug in the times for David and Alex alone:
+
= 
Find the least common denominator, which is 40.
+
= 
= 
Cross multiply and solve for T:
9T = 40
T = 40/9
So, if they worked together, it would take them 40/9 hours
Answer:
112.491 = one hundred twelve and four hundred ninety-one
thousandths.
Step-by-step explanation: