Manhattan GMAT Word Translations Book 4th edition Page 87

[beyice]

Hi, I got a question on page 87 Word Translations book 4th edition

how to get: P(one roll) + P(two rolls) + P(three rolls) =

1/6 + (5/6 . 1/6) + (5/6 . 5/6 . 1/6)

I'm guessing that for P(one roll) equal to 1/6 because molly roll a 1 on her first attempt which means she must stop therefore 1 (number of successful outcome) divided by 6 (possibilities), but I cannot understand why the second and third roll is equal "(5/6 . 1/6) + (5/6 . 5/6 . 1/6)".

Can someone help me?. Thank you. And sorry if my question kinda stupid, I'm a noob :(.

Cheers

[gayathri248]

1/6 + (5/6 . 1/6) + (5/6 . 5/6 . 1/6)

2nd term
5/6 refers to the first unsuccessful attempt P(undesired outcome) = 5/6 and the 1/6 means that the second attempt was successful

3rd term -- on similar lines above first and second attempts were unsuccessful (5/6*5/6) and the third one was successful so 1/6 at the end

there is no fourth term because the question limits it to 3 attempts

[tim]

Good explanation, Gayathri. Beyice, let us know if you still need further help on this problem..