Top menu: NT = Number Talks PT = Pattern Talks (hover over NT to see)

**21. A pair of jeans costs $60. The sales tax is 8.25%. What is the total cost for the pair of jeans?**

**Student 1**

- I rounded 8.25% to 10%, 10% of $60 is 6, so the total cost is $66. But I know the answer is slightly lower because I’d rounded up.

**Student 2**

- I knew 10% would be $6, so the tax is less than that. Then I just ignored the % sign and the 0 in 60, so that the math I did mentally was 825 times 6. I got 4950. Since I knew the answer was less than 6, I knew the number I wanted was $4.95. Add this to $60, that’s $64.95.

**Student 3**

- 8% of $60 is $4.80
- .25% of $60 is 15 cents
- Add above to get $4.95

Student 4

Student 4

- I set up the problem as 2 fractions being multiplied: (60/1) × (8/100) = 480/100 = 4.8. Add 60 to 4.8, that’s $64.8, but since I rounded the 8.25% to 8%, I think the answer is closer to $65.

**22. Three corn dogs cost $5.25. How much does one corn dog cost?**

*I asked this question because Justin Lanier shares how he and his friend had done this math problem mentally.*

**Student 1**

- I just divided like I normally would on paper. Yea, I just set it up in my head because it’s not too bad.

**Student 2**

- I knew that if the price had been $6, then each corn dog would cost $2. But it costs 75 cents less than that, so 75 divided by 3 is 25. I subtracted 25 cents from $2 to get $1.75 for each.

**Student 3**

- I knew each must cost at least $1. Then I split up the leftover $2.25 into thirds: three 25-cents are not enough, three 50-cents are still not enough, so I tried three 75-cents, and that added up to $2.25.

**Student 4**

- I used the divisibility rule to see if $5.25 is divisible by 3: 5+2+5 = 12, and 12 is divisible by 3, so I knew the amount is divisible by 3. I just tried some numbers and $1.75 works.

**Student 5**

- I changed $5.25 to 21 quarters. 21 divided by 3 is 7 — 7 quarters is $1.75.

**Student 6**

- I tried $1.50 first, that got me $4.50 for 3 corn dogs. I tried $2, and that’s $6 total. So I tried the middle number of $1.75, and it worked.

*When I shared with the students how Mr. Lanier had done the problem, they said they would never have guessed that! I said to them, “Math Munch people are just cool like that.” :)*

**23. Would you rather... **

**Student 1**

- I’d choose 50 acre at 42%.
- I changed 58% to 66% because 66% is 2/3, and 2/3 of 30 [acre] is 20.
- I did 50% of 42 is 21.
- I bumped up step 1 to 66% and it’s still lower than the 2nd step (20 versus 21), so I know the 2nd option is higher.

Student 2

Student 2

- I chose the 30 acre at 58% because…
- 60% of 30 is 18.
- 40% of 50 is 20.
- Even though 20 is higher than 18, I’m wasting 30 acres of land [50 minus 20], and with the other one [18], I’m wasting only 12 acres [30 minus 18].

Student 3

Student 3

- I agree with and my math is the same as Ss2’s. A lot of water is wasted on the larger 50-acre plot because of the lower survival percentage.

**Student 4**

- I compared the two percentages with each other and the two acres with each other.
- There’s a 2/5 difference between 30 and 50 acres. And 2/5 is 40%. So, I’m gaining 40% in land.
- 58% minus 42% is 16%, so I’m losing only 16% of the survival rate.
- This is why I’d chose the 50-acre plot.

**24. Would you rather... **

**Student 1**

- I chose to drive 1.2 miles because it’s only 0.9 miles more, and 18 cents per gallon cheaper seems to make the extra driving worth it.

**Student 2**

- Depends on the MPG of the car.

**Student 3**

- Not enough information. I’d need to know how many gallons are in the tank.

**Student 4**

- My family’s car can take 12 gallons, so I’d go 1.2 miles because 18 cents per gallon times 12 gallons is worth it.

**Student 5**

- What if I just wanted to add 1 gallon to the tank? So I don’t mind the extra 18 cents. (When he shared this with the class, someone responded with, “Really?? What idiot would pull up to just get one gallon?” Rough crowd.)

**Student 6**

- Modern cars have better MPG, so the 0.9 extra miles won’t be a big deal and I’d save in gas overall.