What is the difference between the greatest and smallest four-digit numbers that can be formed by the digits 6, 4, 5, and 9 such that the digit 6 is always at the ones place and no digit is repeated?

The given digits are 6, 4, 5, and 9. Here, 4 < 5 < 6 < 9 We have to form a four-digit number such that digit 6 is always at the ones place. In order to form the greatest four-digit number, we have to place digits 9, 5, and 4 at the thousands, hundreds and tens place respectively and 6 at the ones place.  Therefore, the number so formed is 9546. Similarly, the smallest four-digit number will have 4 at the thousands place, 5 at the hundreds place, 9 at the tens place, and 6 at the ones place. The number so formed is 4596. Therefore, the smallest and the greatest numbers that can be formed by the digits 6, 4, 5 and 9 such that digit 6 is always at the ones place and no digit is repeated are 4596 and 9546, respectively. Hence, the required difference is 9546 - 4596 = 4950 The correct option is (4).