Answer:
the first friend
Step-by-step explanation:
It is important to remember that a core is the brain of the CPU (central processing unit), which means one who has a dual-core is having "a dual brain" to process information faster.
Consider also, IT experts often acknowledge that in terms of speed of execution, it is proven that, "dual-core systems" are faster (even twice faster) than a "single-core system". The other friends were wrong because they disagreed with a widely accepted fact that dual-core is faster than single-core; and of course, we know that without them being faster they can't run twice the applications and twice the data.
Therefore, we can make the conclusion that the first friend's response is correct.