Games & Puzzles

Secret Number

A simple calculator showing 0.

Materials:

  • simple calculator (smart phone, tablet or computer calculator will work)

Annie and Ben are playing. Annie puts her secret number into the calculator without showing Ben.
Annie then asks Ben, “What single digit number do you want to add?”
Ben tells Annie the number he wants to add.
“I want to add four.”

Annie presses the ‘add’ button and then the four button. The calculator now shows ‘4’. Annie gives the calculator to Ben.
Ben presses the ‘equals’ button and the calculator gives the answer ’10’.

What was Annie’s secret number?
How do you know?

You could play this with a friend. If you figure out the other player’s secret number correctly, it is your turn to put in a secret number of your own.
You could score a point for every one you get right.

Possible Adaptation:

You could start with a 2 digit secret number and ask “What single digit number do you want to subtract?” Then press the minus button and the number. Give the calculator to the other player and have them press the equals button and ask them to tell you what your secret number is.

Adapted from nrich.maths.org

100 Square Jigsaw Puzzles

Jigsaw puzzle pieces turned over and spread out.

Materials:

  • access to technology (laptop, computer, smartphone, tablet etc.)

Try to solve these online 100 Square Jigsaw Puzzles.

Puzzle #1 probably seems familiar but you may need to think “outside the box” to solve the other puzzles.

Possible Hints/Questions

Which piece has the lowest number?
Which piece has the highest number?
How could that help you solve the puzzle?

Can all 4 puzzles be called 100 squares? Why?