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The OP is wondering about problem #9. It's from a 4th grade math class.
Everybody agrees that the first "is" is a typo.
My contention is that there is no pattern--there is exactly one number that satisfies the problem as written. x=3x-1. Therefore, x=1/2. There is no pattern, and no fourth number.
A couple of other people are arguing in favor of a sequence defined by
and then picking what would be the fourth element in either
or
.
Thoughts?