Problem Solving

What is the sixtieth term in the following sequence? 1, 2, 4, 7, 11, 16, 22...
(A) 1,671
(B) 1,760
(C) 1,761
(D) 1,771
(E) 1,821

praveen_gmat wrote:What is the sixtieth term in the following sequence? 1, 2, 4, 7, 11, 16, 22...
(A) 1,671
(B) 1,760
(C) 1,761
(D) 1,771
(E) 1,821

Every term increases in the following pattern
1 2 4 7 11 16
First diff = 1
2nd diff = 2
3rd diff = 3 and so on
to find the sixtieth term,just find the sum of the numbers increasing by differences + 1
for example,In the sequence provided 5th tem is 11
to get this we take sum of first four natural numbers which is 10 + 1 =11
similiarly to find 60th term take sum of 59 natural numbers + 1 =1771
Pick D

My Ans : D 1771

@ aloneontheedge...

I understood your solution .. but guess you made a calculation mistake .. 1771 is the answer.

Thanks for the help !

Pattern is: 1 2 4 7 11 16 22 29
Differences are: 1 2 3 4 5 .....

Thus each term in the sequence can be defined as tn = Sigma(n-1) + 1
Thus t60 = (59*60)/2 + 1 = 1770 + 1 = 1771.

D is the answer.

praveen_gmat wrote:@ aloneontheedge...

I understood your solution .. but guess you made a calculation mistake .. 1771 is the answer.

Thanks for the help !

So stupid i am, will correct it. thanks for pointing it out