Fun with Numbers & Puzzles

Special Numbers Puzzle

Consider these four numbers: 9, 16, 25, 43. Which one is different? Actually, all of them can be special!

• 9: The only single-digit number.
• 16: The only even number.
• 25: The only multiple of 5.
• 43: The only prime number.

This shows that “special” depends on the rule you are looking at!

A Prime Puzzle

Imagine a grid where the product of rows and columns must match specific numbers.

If the product is 75 and one number is 5, the missing part is $75 \div 5 = 15$. If the missing part must be prime numbers multiplied, then $15 = 3 \times 5$. So the row might be: 5, 3, 5.

Leap Years

A year is a Leap Year if:

1. It is divisible by 4.
2. UNLESS it is divisible by 100 (century year), in which case…
3. It must also be divisible by 400 to be a leap year.

• 2024: Divisible by 4? Yes. (Leap Year)
• 1900: Divisible by 4? Yes. Divisible by 100? Yes. Divisible by 400? No. (Not a Leap Year)
• 2000: Divisible by 400? Yes. (Leap Year)