The greatest number of four digits which is divisible by each one of the numbers 12, 18 21 and 28 is?

Required number is divisible by the L . C . M of 12, 18, 21, 28 i.e 252.
Now, greatest number of four digits = 9999
On dividing 9999 by 252, the remainder is 171
∴ Required number = (9999 - 171) = 9828.