1. Find the square numbers from the list given below.

5, 9, 12, 16, 50, 60, 64, 72, 80, 81

Ans: 9, 16, 64, 81, 4, 25, 49 are square numbers.

2. Which are the triangular numbers in the given list?

3, 6, 8, 9, 12, 15, 16, 20, 21, 42

Ans: 3, 6, 15, 21, 28, 10, 45, 55 are triangular numbers.

3. Name a number which is square as well as triangular.

Ans: 1 and 36 are square as well as triangular number.

4. If 4 is the first square number, which is the tenth one?

Ans: Square numbers are – 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, …

So if 4 is the first square number then the tenth square number will be 121.

5. If 3 is the first triangular number, which is the tenth one?

Ans: Triangular numbers are – 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, …

So if 3 becomes the first triangular number then the tenth triangular number will be 66.