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25 Mar 2026, 14:30
Kudos
Bookmarks
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
75%
(hard)
Question Stats:
50% (02:34) correct
50%
(02:11)
wrong
based on 30
sessions
History
Date
Time
Result
Not Attempted Yet
Giannis and Dinos run a 10-kilometer race. Giannis runs three times as fast as Dinos. If Giannis finishes the race \(m\) minutes faster than Dinos, what is Giannis’s average speed, in kilometers per hour?
A. \(\frac{400}{m}\)
B. \(\frac{600}{m}\)
C. \(\frac{2000}{3m}\)
D. \(\frac{1200}{m+3}\)
E. \(\frac{1200}{m}\)
A. \(\frac{400}{m}\)
B. \(\frac{600}{m}\)
C. \(\frac{2000}{3m}\)
D. \(\frac{1200}{m+3}\)
E. \(\frac{1200}{m}\)
25 Mar 2026, 23:58
Kudos
Bookmarks
Classic rate problem with an algebraic twist. Work it in terms of Giannis's speed and you get there quickly.
1. Let Giannis's speed = v km/h. Since Giannis runs three times as fast as Dinos, Dinos's speed = v/3 km/h.
2. Time for Giannis to finish 10 km = 10/v hours = 600/v minutes.
3. Time for Dinos to finish 10 km = 10/(v/3) = 30/v hours = 1800/v minutes.
4. Giannis finishes m minutes faster, so 1800/v - 600/v = m. That gives 1200/v = m, so v = 1200/m.
Answer: E.
The trap here is picking B (600/m). A lot of people plug Giannis's time alone into the equation instead of the time difference. "600/v = m" feels right when you're moving fast, but m is the gap between the two runners, not Giannis's finishing time.
Also: "three times as fast" means Dinos's speed is v/3, not 3v. Giannis is the fast one. I've seen people flip this and end up with nonsense.
1. Let Giannis's speed = v km/h. Since Giannis runs three times as fast as Dinos, Dinos's speed = v/3 km/h.
2. Time for Giannis to finish 10 km = 10/v hours = 600/v minutes.
3. Time for Dinos to finish 10 km = 10/(v/3) = 30/v hours = 1800/v minutes.
4. Giannis finishes m minutes faster, so 1800/v - 600/v = m. That gives 1200/v = m, so v = 1200/m.
Answer: E.
The trap here is picking B (600/m). A lot of people plug Giannis's time alone into the equation instead of the time difference. "600/v = m" feels right when you're moving fast, but m is the gap between the two runners, not Giannis's finishing time.
Also: "three times as fast" means Dinos's speed is v/3, not 3v. Giannis is the fast one. I've seen people flip this and end up with nonsense.
