Question

What are the last two digits in the square of 39?

• A. 21
• B. 31
• C. 41
• D. 11

Answer 1

The correct option is A 21

We'll use the proximity to 50 method.
First, subtract 25 from 39
$\Rightarrow 39-25=14$.
Next, subtract 39 from 50 and square the result.
$\Rightarrow (50-39{)}^2=(11{)}^2=121$.
Since the last two digits are only taken while using the proximity to 50 method,
1 is a carryover and is added to 14.
$\therefore {39}^2=[14+1]21=1521$
Hence, the last two digits are 21.