# Thread: Probablity of price increase or decrease

1. ## Probablity of price increase or decrease

Let the probability that the FTSE 100 increases today be 0.6 and the probability it goes up tomorrow be 0.7, and the probability that it increases both today and tomorrow be 0.50 Find the probability that it goes down or remains the same both today OR tomorrow.

So is the question asking for: .$\displaystyle P(A' \cap B')$=1- .$\displaystyle P(A \cap B)$=0.50 is this correct?

2. Originally Posted by charikaar
Let the probability that the FTSE 100 increases today be 0.6 and the probability it goes up tomorrow be 0.7, and the probability that it increases both today and tomorrow be 0.50 Find the probability that it goes down or remains the same both today OR tomorrow.

So is the question asking for: .$\displaystyle P(A' \cap B')$=1- .$\displaystyle P(A \cap B)$=0.50 is this correct?

$\displaystyle P(A)=.6$,

$\displaystyle P(B)=.7$, and

$\displaystyle P(A\cap B)=.5$.

And we seek $\displaystyle P(A\cup B)=P(A)+P(B)-P(A\cap B)=.8$.

However, your initial statement of the question seems unclear, so maybe that's not what you are asking.

3. I think you worked out probability of increase today or tomorrow. I want to find the probability of decrease today or tomorrow. thanks for your help.

4. Originally Posted by charikaar
I think you worked out probability of increase today or tomorrow. I want to find the probability of decrease today or tomorrow. thanks for your help.
Ah, okay. Well, then we wish to find $\displaystyle P(A'\cup B')=P[(A\cap B)']=1-P(A\cap B)=.5$.

So, yes, you are correct (except for notation).