The mode of a series of five numbers is 3, the median is also 3 and the mean is four
There are five possibilitys of the numbers in the series
What are they

What do YOU think ?
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My dad always had the most annoying answer to this kind of thing, But I think it really would help you;
Look up all the words in the question that you don't understand.
What is a mode? Series of 5 = 3
what is a median series of 5 = 3
what is a mean series of 5 = 4

Sounds like they want 5 numbers that could be in this series

You could call these mystery numbers by letters
A B C D E
We know that 3 and 4 have to be in the series, But their location is unknown. The definitions of the 3 terms will tell you where to place them and what the other terms are in the series.

Math is easy if you do the work to understand it, have fun!