Problem Solving - Require Assistance

Question

The question is not clear. How many of the products are positives depends on numbers picked at the first plac.

kichha51 · Answer

bellcurve is right! not much info is available to solve this.

Regards,
Vijendra

fluke · Answer

5 +ves.
4 -ves.

We get positive product if we choose:
2 -ves AND 1 +ve
OR
0 -ves AND 3 +ve

So,
 C^4_2*C^5_1+C^4_0*C^5_3=6*5+1*10=40

Ans: "C"

kichha51 · Answer

fluke,

can you please explain. I didn't get it.

fluke · Answer

+*+*+= +ve
-*-*+= +ve

Thus, if we select 3 positive numbers; their product will be +ve.
OR
If we select 2 -ve numbers AND 1 +ve number, their product will also be +ve.

We know there are:
5 +ve numbers
4 -ve numbers

Thus,
Select 3 positives out of 5 positive number
+
Select 2 negative number out of 4 negative AND 1 +ve out of 5 positive numbers.

In combination, we can write
C(5,3)+C(4,2)*C(5,1)

kichha51 · Answer

Thanks for the clarification fluke.

l0rrie · Answer

Pff I was on the right track but I multiplied the results.. Why the ... would someone do that lol

puneetj · Answer

does it matter if the numbers are not distinct? I would still get the same answer, right?

fluke · Answer

No, it doesn't matter. Yes, you will get same answer.
-1,-1,-1,-1,1,1,1,1,1
-1,-2,-3,-4,1,2,3,4,5
Same results.

puneetj · Answer

Thanks for the clarification fluke

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