My ans is also C.17.
1 also gives 1 remainder when divided by 3, another number is 4, then 7 and so on.
Hence we have an arithmetic progression: 1, 4, 7, 10,..... 49, which are in the form 3n+1.
Now we have to find out number of terms.
tn=a+(n-1)d, where tn is the nth term of an AP, a is the first term and d is the common difference.
so, 49 = 1+(n-1)3
or, (n-1)3 = 48
or, n-1 = 16
or, n = 17
I like this solution using the arithmetic progression but in the expression tn=a+(n-1)d
and not n
As I know Un= U0 + n r where U0 is the first terme and r is the common difference.
Thx in advance for the lighting !
The Kudo, please