Which one is the greatest among 1902, 1920, 9201, 9210?
9210
Among all the given four digit numbers, the greatest number should have biggest digit at the Thousand's place.
There are two such numbers 9201 and 9210
Among these two numbers 9210 has 1 at the tens place whereas 9201 has 0 at the tens place
So, 9210 is the greatest number.