MATH TRICK - SQUARE A NUMBER ENDING IN 5

 

To square a number ending in 5 quickly, you can use this trick:

1. Take the number ending in 5: For example, 25.
2. Remove the 5 and note the remaining number: For 25, the remaining number is 2.
3. Multiply the remaining number by the number plus one: For 25, multiply 2 by 3 (2 + 1).
   • $2 \times 3 = 6$.
4. Append 25 to the result: This gives you 625.

So, $25^2 = 625$.

General Formula: For any number $n$ ending in 5, which can be expressed as $10a + 5$:

1. Compute $a \times (a + 1)$.
2. Append 25 to the result.

For instance:

• To square 45:
  1. Remove the 5, leaving 4.
  2. Multiply 4 by 5 (4 + 1): $4 \times 5 = 20$.
  3. Append 25 to get 2025.

Thus, $45^2 = 2025$