# Thread: Probability and Surface Area help needed

1. ## Probability and Surface Area help needed

I need help on q3 a and b when you click this link

Key Maths: Summary and Practice ... - Google Book Search

Please could you help me by showing the working out

I also need help on this probability question. I've worked out the first part which is 7/15 i think but I do not know how to do the 2nd part.

Its q2 at the bottom of the page

Key Maths: Summary and Practice ... - Google Book Search

Thank you

2. Originally Posted by Bananas92
I need help on q3 a and b when you click this link

Key Maths: Summary and Practice ... - Google Book Search
What have you done so far? Do you know the formulas for slant area of a cone and surface area of a sphere? Have you found the height of the cone?

Please could you help me by showing the working out

I also need help on this probability question. I've worked out the first part which is 7/15 i think but I do not know how to do the 2nd part.

Its q2 at the bottom of the page

Key Maths: Summary and Practice ... - Google Book Search

Thank you
There are 10 counters, 4 are red and 6 are blue. The probability the first counter drawn is red is 4/10= 2/5. Given that, there are now 3 red and 6 blue counters. The probability the second counter drawn is also red is 3/9= 1/3. The probability the first two counters drawn are both red is (2/5)(1/3)= 2/15.

The probability the first counter drawn is blue is 6/10= 3/5. Given that,there are now 4 red and 5 blue counters. The probability the second counter is also blue is 5/9. The probability the first two counters draw are both blue is (3/5)(5/9)= 1/3.

The probabilty they are the same color (both red or both blue) is 2/15+ 1/3= 2/15+ 5/15= 7/15.

Now you try the other ones.