I wrote about the 2/3 Rule here. Below is the worksheet I used with my class.

The 2/3 Rule Name _
You have a friend who exaggerates about everything. If he runs 2 miles, he’ll say he ran 3. If he says he did 15 problems for homework, it was probably more like 10. However, it’s easy to figure out the actual number if you use the 2/3 rule.
When you know that he is under-exaggerating (the actual number is bigger), just divide the number by 2/3.
40 minutes ÷ 2/3 = 60 minutes
When you know that he is over-exaggerating (the actual number is smaller), just multiply the number by 2/3.
3 miles x 2/3 = 2 miles

Figure out the actual number given what this student says: actual number
1. “I bought this game and it was really cheap. It was only $40.”

2. “It won’t take me too long to get ready. Maybe 20 minutes.”

3. “I had a great party at my house last night. There were 120 people there!”

4. “That homework took forever. I spent 6 hours on it. I hate my math teacher.”

5. “I’m so tired. I only got 3 hours of sleep.”

6. “I love that book. I read it so fast that I finished it in five days.”

7. “I didn’t eat the whole bag of Oreos. I only had about 10.”

8. “I caught a huge fish the other day. It was fifteen inches long.”

9. “That kid is stalking me. He sent me 1,200 texts last week.”

10. “No, honey. I didn’t date that many girls. I might have dated eight altogether.”