Since a decimal number is called "significant" if each of the digits is greater than 5. We have 256, 4-digit significant numbers
A decimal number is called "significant" if each of the digits is greater than 5. To find how many 4-digit "significant numbers are there, we proceed as follows
To solve the problem, we use a permutation since this requires an arrangement of numbers.
Now, since a decimal number is called "significant" if each of the digits is greater than 5 and we require a decimal with 4 digits that are significant. Now, since the digit has to be greater than 5, there are 4 digits which are greater than 5 and they are 6, 7, 8 and 9.
Since we have 4 slots for the 4 digits, the arrangements are 4 digits in the first slot, 4 digits in the second slot, 4 digits in the third slot and 4 digits in the fourth slot.
So, we have 4 × 4 × 4 × 4 = 256
So, we have 256, 4-digit "significant numbers