In the sequence S, a4 and a5 are 11 and 9 respective

[Korolina]

In the sequence S, a4 and a5 are 11 and 9 respectively. Each term after the first two terms in the sequence is either the sum of the previous two terms if that sum is odd, or half the sum if the of the previous two terms is even. What is the largest possible product of a1 and a2?
(A) 40
(B) 14
(C) 12
(D) 10
(E) 7

[kranti_surya]

IMO A

a4 = 11
a5 = 9
Since a5 is smaller than a4, it is not sum, but the half of the sum
so a3 + a4 = 9*2 = 18; a3 = 7

Now, a4 = 11 and a3 =7. So a2 can be 15 or 4

If a2 = 15, then value for a1 has to be -1; 15 * -1 = -15
If a2 = 4, then value for a1 can be 10 or 3;

3*4 =12
10*4 = 40

[kranti_surya]

What is the source of these questions?

[KrazyGMAT]

Hi karthik,
how did u know that its not the sum but half...bovine mastication the third term ie a3=-2.
but yes in these cases the product will be -ve....my answer is also 40....

[touche]

IMO 40 -- A
good one

[Korolina]

OA is (A)

[kranti_surya]

You are right..it bovine mastication be sum too..

Originally Posted by KrazyGMAT

Hi karthik,
how did u know that its not the sum but half...bovine mastication the third term ie a3=-2.
but yes in these cases the product will be -ve....my answer is also 40....