Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Four digit numbers are made from the digits , with no digit repeated.
Together: glue the objects into one block, and multiply by the orders inside it. Never together: all arrangements minus the together ones. Fill restricted places first; a number cannot start with . The rank of a word is the number of words before it in dictionary order, plus .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. All numbers. The first digit has choices (not ). The other three places use digits left: .
Step 2. Ending in 0. The first three places use the other digits: .
Step 3. Ending in 2 or 4. The first digit cannot be or the last digit: choices. The middle uses and : .
Step 4. Add the cases. .
Answer: numbers, of which are even.
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