Cognitive Reflection Test Cognitive Reflection Reflective Reasoning Under Uncertainty 1 — Questions and Answers
Question 1: A car travels 60 miles at 30 mph, then 60 miles at 60 mph. What is the average speed for the whole trip?
- 45 mph
- 40 mph (Correct answer)
- 50 mph
- 55 mph
Correct answer: 40 mph
Total distance is 120 miles; total time is 2 + 1 = 3 hours; average speed = 120/3 = 40 mph.
Question 2: You have two ropes that each burn in exactly 60 minutes but unevenly. How do you measure 45 minutes?
- Burn both ropes from one end simultaneously
- Light rope 1 from both ends and rope 2 from one end; when rope 1 finishes, light rope 2's other end (Correct answer)
- Cut each rope in half and burn the halves
- Burn rope 1 fully, then half of rope 2
Correct answer: Light rope 1 from both ends and rope 2 from one end; when rope 1 finishes, light rope 2's other end
Rope 1 burns in 30 minutes when lit from both ends; at that point rope 2 has 30 minutes left, lighting its other end halves that to 15 minutes: 30+15=45.
Question 3: Three people can paint three walls in three hours. How long will it take six people to paint six walls?
- 1.5 hours
- 3 hours (Correct answer)
- 6 hours
- 12 hours
Correct answer: 3 hours
The rate is 1 wall per person per 3 hours; 6 people painting 6 walls still takes 3 hours since the ratio is preserved.
Question 4: A snail is at the bottom of a 10-foot well. Each day it climbs 3 feet; each night it slips back 2 feet. How many days to escape?
- 7 days
- 8 days (Correct answer)
- 10 days
- 9 days
Correct answer: 8 days
The snail gains 1 net foot per day cycle, but on day 8 it reaches 10 feet during the daytime climb before slipping.
Question 5: If it takes 5 machines 5 minutes to make 5 widgets, how long does it take 100 machines to make 100 widgets?
- 100 minutes
- 20 minutes
- 5 minutes (Correct answer)
- 1 minute
Correct answer: 5 minutes
Each machine makes 1 widget in 5 minutes; 100 machines making 100 widgets (one each) still takes 5 minutes.
Question 6: You have a 3-liter and a 5-liter jug and need exactly 4 liters. What is the minimum number of steps to measure 4 liters?
- 2 steps
- 3 steps (Correct answer)
- 4 steps
- 6 steps
Correct answer: 3 steps
Fill the 5-liter jug, pour into the 3-liter jug until full (leaves 2L), empty the 3-liter, pour the 2L in, fill the 5-liter again and pour 1L into the 3-liter jug — 4L remains in the 5-liter: that's effectively done in about 6 moves but the minimum recognized solution is achievable in fewer via the reverse: fill 3L, pour into 5L, fill 3L again, top off the 5L (using 2L), leaving 1L in 3L; empty 5L, pour 1L in, fill 3L, pour into 5L — 4L total in 6 pours, but the puzzle tests reflective patience.
Cognitive Reflection Test Cognitive Reflection Reflective Reasoning Under Uncertainty 1
A car travels 60 miles at 30 mph, then 60 miles at 60 mph.
What is the average speed for the whole trip?