Question

Find the value of $19\times 21$ using odd-even property.

• A. 399
• B. 299
• C. 199
• D. None of these

Answer 1

The correct option is A 399

$19\times 21=(20-1)$ $\times$ $(20+1)$

$=$ $400$ $+20-20-1$ $=$ $399$

Hence, option A is correct.