Determine the greatest 4-digit number whose digits are different and units’ digit is 7.
You can make a 4-digit number with 4 numbers.
Put the greatest number (9) in the thousands place.
Put the next greatest number (8) in the hundreds place.
Put the next greatest number (6) in the tens place. You cannot use 7 in the tens place, because that number belongs in the units place.
Put the number 7 in the units place.
So, the greatest number is .