Number (place value): Penguin Thief
The Problem
On an Antarctic beach, Arwel the Adélie penguin had just completed his nest, which was made from stones. He was very proud of his nest. He hoped that its impressive size would help him attract a mate. After his hard work, he was feeling very hungry and headed out to sea to catch a fish supper. While he was hunting for food, a greedy Adélie penguin called Ralph stole some of Arwel’s stones for his own nest.
Can you use the clues below to work out exactly how many stones Ralph stole?
Clues
1) The number is below 50.
2) The number is an odd number.
3) The sum of the number’s digits is 7.
4) The number is 3 away from a multiple of 10.
Did you need to use all the clues? Why or why not?
Visualising the Problem and Getting Started
You will be given a number square like the one below. Crossing off any numbers that cannot be the answer is a great way to approach this problem. Before you get started, familiarise yourself with the 100 square and see how quickly you can find the following:
- The four numbers covered by an Adélie penguin
- A multiple of 5 that is greater than 20 but less than 30
- A number whose sum of its digits is 14 and whose tens digit is the same as its ones digit
