Hi Rajorshi100,
This DS question involves a specific sequence called a "Fibonacci" sequence. A Fibonacci sequence adds 2 consecutive terms to figure out the "next" term.
As an example, here's a traditional Fibonacci sequence: 1, 1, 2, 3, 5, 8, 13, 21, etc.
1+1=2
1+2+3
2+3=5
3+5=8
etc.
The language in this sequence ("each term after S2 is equal to the stun of Sn-1 + Sn-2") describes a Fibonacci sequence. It's worth noting that this type of sequence can start with ANY 2 numbers.
We're told that the 1st term = 4. We're asked for the value of the 2nd term.
Fact 1: The 3rd term = 7
With this info, we know....
1st term + 2nd term = 3rd term
4 + 2nd term = 7
We can calculate that the 2nd term = 3
Fact 1 is SUFFICIENT
Fact 2: The 4th term = 10
From the prompt, we know that...
1st term + 2nd term = 3rd term
4 + 2nd term = 3rd term
With the info from this Fact, we know...
2nd term + 3rd term = 4th term
2nd term + 3rd term = 10
We end up with 2 variables and 2 unique equations:
4 + 2nd term = 3rd term
2nd term + 3rd term = 10
This is a "system" of equations and we CAN solve it with algebra (since it's a DS question, we don't have to though).
Fact 2 is SUFFICIENT
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
