Distance problems is back
Algebra
Level
3
John travels by car daily to reach his office. If John increases his speed by 10 km/hr, his travel time is reduced by 1 hour. If John decreases his speed by 20 km/hr, his travel time increases by 8 hours. At what speed John needs to travel if he needs to reach his office by 2 hours?
The answer is 60.
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1 solution
If John drives at his usual speed of v for a distance of d, he reaches his office at t , or simply put, d/v=t (( equation 1)
If he increases his speed by 10, he arrives one hour early. Simply put, d/(v+10)=t-1 ( Equation 2)
If he reduces his speed by 20, he is late by 8 hrs. Simply put, d/(v-20)=t+8 ( Equation 3)
Solve this simultaneous equation. d=120 km, t=4 hours and v=30 km/h