What is the Probability of Throwing Two Dice and Getting Specific Numbers?

[desmond iking]

Homework Statement

A pair of dice are thrown. If a die show number 6 , what is the probability of (a)another die show number 2? (b) total score for both number greater than 8 ?

for part (a) , my working is 1/6 x 1/6 = 1/36

but actual ans is 2/11 for part (b), the ans is 7/11

Homework Equations

The Attempt at a Solution

 

[LCKurtz]

Homework Statement

A pair of dice are thrown. If a die show number 6 , what is the probability of (a)another die show number 2? (b) total score for both number greater than 8 ?

for part (a) , my working is 1/6 x 1/6 = 1/36

but actual ans is 2/11 for part (b), the ans is 7/11

Homework Equations

The Attempt at a Solution

Write down all the outcome pairs where at least one die shows a 6. How many such pairs do you have? How many of those pairs also include a 2?

 

[desmond iking]

(1,6) , (2,6) , (3,6) , (4,6) , (5,6) , (6,6)

one contain (2,6)

 

[LCKurtz]

What about (6,1),(6,2) etc.?

 

[desmond iking]

What about (6,1),(6,2) etc.?

hi, i got the solution now. but i just can't understand why i can't use the probability tree to get the ans as the photo below?

 

[vela]

You drew a tree, but you haven't shown getting an answer to the question using it. What answer do you think the tree is leading you to?

 

[haruspex]

A pair of dice are thrown. If a die show number 6 , what is the probability of (a)another die show number 2?

Is that the exact wording? If so, it's a terrible question. As LCKurtz presumed, it almost certainly intended "if at least one die shows a 6", but that's not what it says.
It all hinges on the basis for selecting the die showing a six. The wording suggests that the observer picked one die at random and saw that it was a six. That will not give 2/11 as the answer.