Shortcut on Squaring A 2-Digit Number Ending In 1:

1. Choose a 2-digit number ending in 1.
2. Subtract 1 from it.
3. Square the difference
4. Add the difference twice to its square(result of step 3).
5. Add 1
   

Example:

Step 1: Choose 41
Step2: 41-1 = 40
Step 3: 40² = 1,600
Step 4: 1,600 + 40 + 40 = 1,680
Step 5: 1,680 + 1 = 1,681

Thus, 41² = 1,681