What is the 4-digit number in which the first digit is one-fifth of the last, and the second and third digits are the last digit multiplied by three?

We'll call this number

We have ⇒

Since is divisible by 5, it is either 0 or 5

But it can't be 0, because then would be 0

So and

Now I'm assuming that the second and third digits are adding to three times the last digit.

So ⇒

We have a number of options:





So the possibilities are:
1695
1785
1875
1965

(If there were another detail we could narrow down the choices further, but otherwise we have all these options.)