Hi,

If you see this number series then you can see that there are two operations happening with the series.

5, 25, 7,______, 9, 19

So the first number is 5 and the 3rd number is 7 then 5th number is 9 which clearly states that numbers are increasing in +2. Whereas 2nd number is 25 then we have to find 4th number and 6th number is 19. 25 > 19 which means numbers are decreasing. we will first see the difference between 25 & 19, which is 6. And then we will divide 6 with 2 i.e. 3. Now we will subtract 25 by 3 and you get 21. And just to confirm we can subtract 21 by 3 and we get 19. So we found the answer of this question.

**Answer***:* 5, 25, 7, **21**, 9, 19