UPSC Prelims 2026 CSAT, question 57

Topic: Series and patterns

Q57

In a sequence of numbers, each number other than the first two is the sum of the two immediately preceding numbers from it. If the first two numbers in the sequence are 4 and 7, then the sixth number is

(a) 29
(b) 37
(c) 43
(d) 47Correct answer

Solution.

Answer: (d) 47

The first two terms are $t_1 = 4$ and $t_2 = 7$ .
Using $t_n = t_{n-1} + t_{n-2}$ , the subsequent terms are $t_3 = 4 + 7 = 11$ , $t_4 = 7 + 11 = 18$ , $t_5 = 11 + 18 = 29$ , and $t_6 = 18 + 29 = 47$ .