SOLUTION: Could someone PLEASE help me with these? I need help badly. Thanks for your time. 1. A plane flies 720 mi against a steady 30-mi/h headwind and then returns to the same point

Question 31725: Could someone PLEASE help me with these? I need help badly. Thanks for your time.
1. A plane flies 720 mi against a steady 30-mi/h headwind and then returns to the same point with the wind. If the entire trip takes 10 h, what is the plane�s speed in still air?
2. Solve for x. 2/5=x-2/20
3. Kevin earned $165 interest for 1 year on an investment of $1500. At the same rate, what amount of interest would be earned by an investment of $2500?

Answer by Paul(988) (Show Source): You can put this solution on YOUR website!
1.
A total distance of 720 miles with x sppeed:
Equation:

Cross multiply

720[(x+30)+(x-30)]=10[(x+30)(x-30)]





Divide the equation by 10:



Use the quadratic formula:

 

a=1, b=-144, c=-900





 --->Remove the negative:



x=150

Hence, the speed of the plane is 150mph.



2.

Multiply the whole equation by 20 and simplfy:



4(2)=20(x)-2

10=20x

x=0.5



3.Simple intest is given by A=(prinicpal * Time * rate)/100 

Let the rate be x:



1500x=16500

x=11 (rate)

A=

x=275

Hence, the rate is 11% and with he same rate the money earned is $275.

Paul.