## mayankdevnani 2 years ago Solve this ONE :- Q-) Problem on SERIES. 6,20,36,48,50,?,0 a)36 b)40 c)46 d)56 Which number comes in place of "?" ?

1. mayankdevnani

@ash2326 @phi @UsukiDoll

56?

3. mayankdevnani

how?

4. UsukiDoll

Ned Flanders

5. mayankdevnani

what?

6. mayankdevnani

Tn = 7n^2 - n^3 T1 = 7(1)^2 - (1)^3 = 6 T2 = 7(2)^2 - (2)^3 = 20 .... ... T6 = 7(6)^2 - (6)^3 = 78 T7 = 7(7)^2 - (7)^3 = 0 so, it is T6 = 78

8. mayankdevnani

but it is not in options. @RadEn

9. mayankdevnani

i know this is also a answer but i need answer which is in options?

10. mayankdevnani

@hartnn can you help me ?

11. hartnn

how did u get Tn RadEn ?

12. SithsAndGiggles

13. mayankdevnani

he makes the series to solve it. @hartnn

14. hartnn

yeah, i know how to find Tn, but i wanted to know whether RadEn used any different/simpler method....

15. mayankdevnani

his method is wrong.

16. hartnn

he got the answer which is in the choices, how u say its wrong ?

17. mayankdevnani

because if we put n=6,the answer comes to be is 36 but in actual(followed by series)the answer would be 50

18. mayankdevnani

isiliye mujhe lagta h ki voh galat h

19. hartnn

" in actual(followed by series)the answer would be 50" what does this even mean ?

20. mayankdevnani

iska matla agar hum uske tarike se follow karien to iska answer 50 aana chaihye series ke hisaab se lekin actual main 36 aa raha h..... iska method thode se hi digits ke liye apply hota h

21. mayankdevnani

now understood @hartnn bhaiya

22. hartnn

lol, i could translate that in hindi myself too

23. hartnn

why u say answer should be 50 ?

24. mayankdevnani

bhaiya , yeh question ntse 2013 RAJ. main poocha gaya tha aur FIITJEE vaalein bata rahein h ki iska answer DATA INADEQUATE h aur CAREER POINT vallein bata rahein h ki iska answer 36 h

25. mayankdevnani

to iska kya answer hoga bhaiya?

26. mayankdevnani

@hartnn

27. hartnn

the answer to this is indeed 36 as shown corretly by RadEn

28. mayankdevnani

29. hartnn

i just wanted to know any simpler way of finding Tn :P

30. mayankdevnani

yeah...this logic doesn't apply in NTSE STAGE 1

31. mayankdevnani

i think there is another logic simpler logic for this

32. hartnn

i think it does apply, the third differences are constant

33. hartnn

|dw:1385197162928:dw|

34. hartnn

so, x - 52 - (-10) = -6

35. hartnn

x= 42 - 6 = 36

36. hartnn

@mayankdevnani @RadEn any simpler way to find Tn ?

wolfram is simpler way , @hartnn hehehe :) why i cant see notification in OS ??

39. hartnn

oh lol but i guess they can't use wolf.... so using the 3rd difference is a simpler manual way...

yeah, just input some numbers in wolfram :)

41. hartnn

and nobody can see notifications its the bug OS admins are trying to fix