27,26

27

2+7=9-4=5+8=13-3=10+9=19-2=17+10=27-1=26

+7,+8,+9,+10

-4,-3,-2,-1

answer:27

2+7=9-4=5+8=13-3=10+9=19-2=17+10=27
27

after a glance we see that 2+3=5 and 5+5=10 again 10+7=17 
so it seems that in this series the digits whihc are adding 
like 2,5 and 7 are going in a order of +2 increasing.
again take the another series :-
9+4=13 and 13+6=19 it is also increasing by +2. so the next 
digit will be 19+8=27.

i have tried to give the best explanation but if there r 
some mistake then pls suggest me.
verma_mukesh1982@yahoo.co.in

2,9,5,13,10,19,17,?

Ans : 27

the difference between the numbers 2 and 5 is 3
lly                                5 and 10 is 5
lly                                10 and 17 is 7

and the difference between the numbers 9 and 13 is 4
lly                                    13 and 19 is 6

so the next sequence number is 8; 19 + 8 = 27

2,9,5,13,10,19,17
if we find the gap b/w sequence no.,we get 7,4,8,3,9,2,10.
now we add 10 in last no. we find 27 i.e, answer.

2,9,5,13,10,19,17
Devide into two sections by taking alternative nos. 
i.e 
2,5,10,17
9(+4)13(+6)19 here next number should be +8 to 19

So the answer is 27

This is a mixup of two different sequences. Alternate 
numbers forma  a sequence. 2,5,10,17,... where odd number 
in the ascending sequence is added. 2+3=5+5=10+7=17 and so 
on. Similarly 9,13,19,... is a sequence where even numbers 
starting 4 is added to every number in increasing 
order.9+4=13+6=19+=27 would be tne next number

The correct answer will be 27....Thanks