SOLUTION: please help me with this two problems. Thank you very much! #1. A jet plane, flying 80 mph faster than a propeller plane, travels 3960 miles in 2 hours less time than the p

Algebra ->  Average -> SOLUTION: please help me with this two problems. Thank you very much! #1. A jet plane, flying 80 mph faster than a propeller plane, travels 3960 miles in 2 hours less time than the p      Log On


   

Question 831327: please help me with this two problems. Thank you very much!

#1. A jet plane, flying 80 mph faster than a propeller plane, travels 3960 miles in 2 hours less time than the propeller plane takes to fly the same distance. How fast does each plane fly?
#2. When the sum of 522 and three times a positive number is subtracted from the square of the number, the result is 126. Find the number.
Found 2 solutions by josgarithmetic, mananth:
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
For #1, I just solved the same exact problem.
See http://www.algebra.com/algebra/homework/Average/Average.faq.question.831317.html


For #2 question,
Let p be the number. highlight_green%28p%5E2-%28522%2B3%2Ap%29=126%29, the symbolic translation from the wording. I leave it there for you to (1) Understand, and then (2) Solve for p. You will want to use the general solution for the quadratic formula.

Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
time taken by propeller plane - time taken by jet = 2 hours for the same distance
t= d/r
d= 3960
speed of propeller = x
speed of jet = x+80

3960%2Fx+-+3960%2F%28x%2B80%29+=2
take LCM
%283960%28x%2B80%29-3960x%29%2F%28x%28x%2B80%29%29=2

3960x +316800-3960x=2x(x+80)
31860=2x^2+160x
2x^2+160x-31860=0
/2
x^2+80x-158400=0
x^2+80x+1600 -1600-158400=0
(x+40)^2=160000
take square root
x+40= 400
x=360 mph speed of propeller plane
speed of jet = 360+80=440 mph