Cognitive Reflection Test Cognitive Reflection Reflective Reasoning Under Uncertainty 1

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?

Accepted Answer

40 mph

Answer

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?

Accepted Answer

Light rope 1 from both ends and rope 2 from one end; when rope 1 finishes, light rope 2's other end

Answer

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?

Accepted Answer

3 hours

Answer

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?

Accepted Answer

8 days

Answer

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?

Accepted Answer

5 minutes

Answer

Each machine makes 1 widget in 5 minutes; 100 machines making 100 widgets (one each) still takes 5 minutes.

Cognitive Reflection Test Practice Test

Cognitive Reflection Test Practice Test

Cognitive Reflection Test Cognitive Reflection Reflective Reasoning Under Uncertainty 1