Hi u2_wa,

In forming a number from the 4 digits,

the even digit may be

__placed__ at the end to make it even,

thus

__forming__ an even number from the digits available.

You don't need to stick to the order the digits came in.

The book answer gives

which is the probability that the

__first__ digit is even,

considering that it doesn't matter whether the others are even or odd.

However, this misses the probabilities of the 1st being odd, the 1st 2 being odd,

the 1st 3 being odd, the 1st and 3rd being odd......etc.