If you toss 3 dices, what is the chance to get at least one 3?

There is a total of 6^3=216 combinations if you roll 3 dice. There are 5^2x3=75 combinations that you will get one 3. Thus there is a 75/216=25/72 chance of getting only one 3 when rolling 3 dice.
There are 5x3 combinations that you will get 2 3s. Thus there is a 15/216=5/72 chance of getting a 2 3s when rolling 3 dice.
There is 1 combination where you will get 3 3s. Thus there is a 1/216 chance you will get 3 3s when rolling 3 dice.
There is a 75+15+1/216=91/216 chance of any of them happening.
This would mean there is a 91/216 chance of at least getting one 3

The answer would be: b

You have 2 sides that are 2 cms and you have 6 sides that are 1/2 cm and you have 4 sides that are 1 cm. the smallest sides are 1/2 the medium sized sides are 1 and the smallest are 1/2. so to find the perimeter you have to add them all up together so your answer will be 11 cm's