Anyone good at maths? (probability)

Stuck with some basic maths probabilty.....

Heres my question guys:

[b]a component is made in 3 stages. the first stage involves building from one of four machines A,B,C and D all with equal probabilites. Second stage is trimmed using one machine either E,F or G, and finally polished using either machine H or J and it is twice as likely to be the former as H works faster[b]

Determine the porbabilty of:

**1. a component is polished on machine H**

* is it 2:1?*

**2. it is trimmed on either machine F or G**

*2/3 or 66%*

[b]3. a component is formed on either machine A or B, trimmed on F and polished on H]/b]

*i have no idea*

**4. it is formed on machine A and polished on J**

*??*

**5. formed on machine B and polished on machine H**

**6. formed on machine A and trimmed on F**

*A = 1/4 or 0.25, F = 1/3 or 0.3*

0.25 x 0.3 = 0.075

0.25 + 0.3 - 0.075 = 0.475 or 47.5%

is that right?

any help on this guys would be a big help, show working out too?

Re: Anyone good at maths? (probability)

Quote:

*Originally posted by adam1v *

*A = 1/4 or 0.25, F = 1/3 or 0.3*

0.25 x 0.3 = 0.075

0.25 + 0.3 - 0.075 = 0.475 or 47.5%

is that right?

any help on this guys would be a big help, show working out too?

no.

1/3=0.333333333

also you multiply for "and" and add for "or", here you seem to do both. Why ?

So as Falcon suggested, 1/4 x 1/3 = 1/12 = 0.083333 = 8.333%