Mrs. Thompson’s class is having a fun math day. She brings in a big jar of jellybeans and tells the students they’re going to play a guessing game. She divides the class into two groups:
Group A: Mrs. Thompson tells them, “There are more than 100 jellybeans in the jar.”
Group B: Mrs. Thompson tells them, “There are more than 500 jellybeans in the jar.”
Each student writes down their guess.
Here are the results:
Group A (15 students):
Lowest guess: 120
Highest guess: 300
Average guess: 210
Group B (15 students):
Lowest guess: 510
Highest guess: 800
Average guess: 650
The actual number of jellybeans in the jar is 375.
1. What’s the difference between the average guesses of Group A and Group B?
2. Which group’s average guess was closer to the actual number of jellybeans?
3. How many more jellybeans did Group B guess on average compared to the actual number?
4. Why do you think the two groups guessed such different numbers?
1. Difference between average guesses:
Group B average – Group A average = 650 – 210 = 440 jellybeans
2. Comparing to the actual number (375):
Group A difference: |375 – 210| = 165
Group B difference: |375 – 650| = 275
Group A’s average guess was closer to the actual number.
3. Group B’s overestimation:
650 – 375 = 275 jellybeans
4. The two groups guessed different numbers because of anchoring bias. The initial information (100 for Group A, 500 for Group B) acted as an “anchor” that influenced their guesses. Group A started thinking from 100 up, while Group B started from 500 up, leading to very different estimates.
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