Determine a Canoe Departure Time
Company: Sig
Role: Data Scientist
Category: Statistics & Math
Difficulty: easy
Interview Round: Online Assessment
# Determine a Canoe Departure Time
Two friends paddle upstream for 3 hours, then realize their campsite is downstream and paddle downstream for 4 hours to reach it. The next day they travel 48 miles upstream from the campsite to their original starting point and arrive at 9:30.
The river current is a constant 3 miles per hour, and the friends' paddling speed relative to the water is constant. At what time did they leave the campsite for the return trip? Express the answer as `h:mm`.
### What a Strong Answer Covers
- Distinction between still-water speed, upstream speed, and downstream speed.
- A displacement equation from the first day's two legs.
- Recovery of the paddling speed from the 48-mile campsite displacement.
- Return duration and subtraction from the arrival time.
### Follow-up Questions
- How would the departure time change if the current were unknown but the return duration were given?
- What minimum still-water speed is required for the upstream legs to be possible?
Overview: Determine a canoe departure time by separating still-water, upstream, and downstream speeds. The worked solution uses the first day's net displacement to find a 27-mile-per-hour paddling speed, then calculates a two-hour return and a 7:30 departure.
Read the full Sig Data Scientist interview experience this question came from