This is a Problem-of-the-Day type blog designed for teachers grades 4 through 8 as an opening and/or closing activity to a classroom lesson. The problems involve computation as well as logical and critical thinking. In my own teaching experience, I have found that many of the problems can be expanded and lead to interesting discussions.

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DAY 1
A man has 10 white socks and 10 black socks in a drawer. They are single socks, not in pairs. The man gets up in the morning while it is still dark. He doesn't turn on the light and cannot see what colors the socks are. What is the least number of socks he must pull out of the drawer to be certain he has a matching pair - either black or white? What is the least number of socks he must pull out of the drawer to be certain he has a pair of each color?

Answer:

To be certain of getting a matching pair of either color, he must pull out 3 socks. He might have a pair after pulling out two, but to be certain, he must pull out 3. He must pull out 12 socks to be sure he has a pair of each color.

DAY 2
Two fathers and two sons were at a picnic. There were only three hamburgers. Yet each person at the picnic ate a whole hamburger. How was this possible.

Answer:

There were only three people at the picnic---a grandfather, a father, and a son. The father is both a father and a son.

DAY 3
A can with 40 mints in it weighed 135 grams. The same can with 20 mints weighed 75 grams. What is the weight of the can?

Answer:

15 grams

DAY 4
A man bought a parrot for $50, sold it for $60, bought it back for $70, and sold it again for $80. How much money, if any, did he make or lose?

Answer:

He makes $20. He makes $10 in each of two separate transactions. He does not lose any money when he buys the parrot back for $70.

DAY 5
How many ways are there to make change for a quarter?

Answer:

12---starting at two dimes and a nickel and ending with 25 pennies