Question

How many different three-digit numbers can be formed by 3 and 5, if none of them is repeated in a number: the answer is 4 can anyone explain it?​

Answer 1

How many different three digit numbers can be formed by 3 and 5 if none of them is repeated in a number?

If we assume 035 and 053 are accepted in the answer, than 48. Otherwise 46.

It's quite easy to reason this out.

You start with 35 and you form all possible combinations adding all digits (except 3 and 5 as per the requirements) to the right:

351 352 354 356 357 358 359 350 = 8 possible; than you repeat putting the extra digit in the middle 315 325 …

You have 8 more in this; repeat one more time, now with the extra digit on the left 135 235… 8 more, totalling 24.

Now you can add 24 more whit 53 thus making 48 (or 46 if 035 and 053 are not accepted answers).