How many three-digit numbers may be formed using elements from the set {1, 2, 3, 4, 5, 6, 7} if no element may be used more than once in a number and the number must be even?

90

Step-by-step explanation:

set: {1, 2, 3, 4, 5, 6, 7} = 7 numbers | 3 even

no element may be used more than once in a number = distinct elements

and the number must be even = must finish with a even number.

This way, we should start with the last number, which we have 3 possibilities.

Since we have 7 numbers in total, we have 6 options for the first one and then 5 options for the second one.

So, we have 6.5.3 = 90

phosphate, calcium ion, chloride ion, neon atom

step-by-step explanation: