Question
Chuong and Hassan both drive 40km from home to work each day. One day, Chuong said to Hassan " If you drive at your usual speed, I will average 40kmph faster than you and arrive home in 20 minutes less time". Find Hassan's speed.
Answers
maribel
do rtd make the distances equal to each other and the speed is 60km well that's what i got but im not very good at these lol
Reiny
Hassan's time = 40/x hours
Chongs time = 40/(x+40) hours
their difference in time is 20 minutes or 1/3 hour
so
40/x - 40/(x+40) = 1/3
multiply each term by 3x(x+40) and simplify to get
x^2 + 40x - 4800 = 0
I used the quadratic formula to get
x = 52.11 mph
check:
Hassan's time = 40/52.11 = .7676 hours
Chong's time = 40/92.11 = .4343 hours
difference in time = .7676-.4343 = .3333 hours = 1/3 hour = 20 minutes
Chongs time = 40/(x+40) hours
their difference in time is 20 minutes or 1/3 hour
so
40/x - 40/(x+40) = 1/3
multiply each term by 3x(x+40) and simplify to get
x^2 + 40x - 4800 = 0
I used the quadratic formula to get
x = 52.11 mph
check:
Hassan's time = 40/52.11 = .7676 hours
Chong's time = 40/92.11 = .4343 hours
difference in time = .7676-.4343 = .3333 hours = 1/3 hour = 20 minutes