Question

Jason and Marie both travel 300 miles. Jason drove at an average speed of 10 miles per hour faster than Marie and made the trip in one hour less time. Find the average speeds of both cars.

Answer 1

jason: 60mph

marie: 50mph

Explanation:

let jason drive at x miles per hour

let marie drive at x-10 miles per hour

let jason drive for y hours

let marie drive for y+1 hours

distance = speed * time

for jason:

300 = x * y

for marie:

300 = (x-10) * (y+1) = x*y + x - 10y -10

300 = x*y

divide both sides by x to solve for y

300/x = y

plug this into the second equation

300 = (x-10) * (300/x+1) = 300 -3000/x +x -10

300 = 300 -3000/x +x -10

subtract 300 from both sides

0 = -3000/x + x - 10

multiply both sides by x to get rid of the denominator

0 = x^2 -10x -3000

factor

0 = x^2 - 60x +50x -3000

0 = x(x-60) + 50(x-60) = (x+50)(x-60)

x = 60 or -50

x cannot be negative so x = 60mph

marie = 60-10 = 50mph