what is next number in sequenc?

Each of the number is divided by 3. Dividing by 3 is the same as multiplying by 1/3.

So the next number would be 1/3 x 1/3 = 1/9

1/9

Keep multiplying by 1/3 (or dividing by 3):

Answer:
1/9

1/9

Look for possible simple Arithmetic Progression (same difference between terms).
9 - 3 --> 6;
3 - 1 --> 2;
1 - 1/3 --> 2/3;
...
No common difference.
So its a "no go" for such a relationship between terms.

Look for a simple Geometric Progression (same factor between terms).
9 * 1/3 --> 3;
3 * 1/3 --> 1;
1 * 1/3 --> 1/3;
...
Click - Rule: multiply previous term by 1/3.
So the solution for the next (aka 5th term) , in this case, would be 1/9.
Calculated as 1/3 (last given term) * 1/3 (common factor) = 1/9.

[The cunning question setter will have thrown in this confusion of a common value (viz. 1/3) deliberately, in order to see whether you can keep the concepts of the term and the factor separate.]


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However, note that no prescriptive formula was designated to guide your solution.
You could be more creative ...

A sequence is just that - a sequential list of things, not necessarily ordered by any relationship, nor being of the exact same type.

The only guidance given is that the solution of the "next" item be a "number".
So, you could choose e.g. "5" or "-12.3456" or "zero" or "pi" or "a googolplex", as valid solutions.

Beyond that you could impose your own restrictive structure.
e.g. assume that the numbers are the Y-values from the graph of a function (symmetric about the Y-axis) taken at X-ordinates (-3,-2,-1,0) - e.g. the parabola 3y = 2 * x^2 + 1.
The "next" Y-value, taken at the "next" X-ordinate = 1, would be y="1".
[So the symmetric sequence would continue as: 9, 3, 1, 1/3, 1, 3, 9, ....]
etc.

N.B. If you wanted to be adventurous in this way then you would need to explain it carefully, else you might not get the "smart" reward you expected from a fraught examiner!
[... and certainly not from an automated one.]

1/9
1/27
1/81

1/9.

"Sequence". 1/9.

1 / 9

1/9?

1/9.