# The Infamous Easter Goblin

## The Activities

Today we had an Easter-themed Math Circle!

1. Topic: Probability: Book: Probably Pistachio by Murphy
2. Topic: Logic: There’s a beautiful egg hidden behind a door numbered 1 – 36. The kids get 10 guesses to find the egg, or else the Easter Goblin gets it. They can ask yes/no questions like: Is it higher than 10?
3. Topic: Combinations: You have a row of 5 Easter eggs. How many different ways can you color 3 out of 5 eggs. i.e. you could color the first 3, or the first 2 + the last one.
4. Topic: Addition: Draw 3 plastic Easter eggs out of a bag. Each egg contains a one or two digit number. Add the numbers together, and the kid with the highest number wins the round.

## Preparation

For the Easter Goblin activity, I colored a few cute paper Easter eggs that the kids would want to save from the silly Easter Goblin (a clipart female goblin).  We printed out a bunch of sheets with 5 egg-shaped ovals on them for the combinations activity.  For the easter egg addition, I used all the left-over plastic easter egg shells, and filled each with a number on a scrap of paper, instead of candy.

## How did it go?

We had 4 kids this week.

#### Easter Goblin

First the kids got 10 questions to find the hidden egg, hidden behind a door numbered 1 – 36. The first kid asked if it was in a door higher than 14. ‘No.’ The next kid asked if it was in a door less than 5.  ‘No.’  The 3rd kid asked if it was number 9.  ‘No.’ The first two kids immediately groaned and said it was not a good question.  I asked why, and they said it’s because it only crossed off one number.  One kid observed that you should ask something more in the middle. Then the 4th kid asked if it was in door number 7.  The first 2 kids again groaned. 🙂

The kids loooved this game, and kept begging for more rounds, but I moved on to the next activity after 4 rounds.

#### Combinations

We did a variation of this activity with the kids a long time ago, and they were not very good at it. This time they had much better strategies. Kid #1 jumped to the lead quickly finding 6 ways to color 3 out of 5 eggs. Kid #2 was right behind.  One strategy #1 and #2 used was to reverse each novel pattern they found, so they would get two at a time.

Kid #2 then moved to the lead, finding a 7th way. This annoyed Kid #1, who sat on the floor for the rest of the activity, making very little progress, but not bothering anyone. Suddenly Kid #3 found a new pattern and had 9 different ways. Kid #4 was just trying all different things, without worrying if some of the patterns were repeats.

Finally Kid #3 found the 10th and last way. Then we compared the other kids papers to find the ones they had missed.  It turned out that Kid #4 unknowingly actually had all 10 patterns among the 26 rows they had colored.