Probability - Coin Tossing

GRE Quant Problem Solving
1

I am a bit confused about this problem.
Coin W is tossed once, and coin X is tossed twice. Both coins are fair.

Quantity A
The probability that coin W returns heads and coin X returns tails twice

Quantity B
0.125

If only one case is considered eg, WXX is considered then the probability is 0.125 or 1/8
Why do we not consider XWX or XXW?
If all 3 cases were considered then won’t the probability be 3/8?
How can I figure out when they want different kinds of tosses and when it’s specific to a single case?

2

Because we are not tossing the same coin thrice. We have

  • one coin W tossed once
  • one coin X tossed twice

Hence,

(W = head) (X = tail) (X = tail) is the same thing as (X = tail) (X = tail) (W = head) - that’s one case.