Correct Answer - Option 3 : 2201
Concept used:-
Trick to multiply two digit numbers ending in 1.
Method:-
- Multiply the left most digits of both the numbers.
- Add the left most digits of both the numbers.
- Put the result from Step(2) next to the result of Step(1)
- Put 1 next to the result of Step(3)
Calculation:-
Let the product be AB1
A = 3 × 7 = 21
B = 3 + 7 = 10
AB1 = 21|10|1
Carryover of B (10) is shifted and added to 21.
Hence, 2201 is our answer.