Explanation:
a probability (or chance) is always the ratio
desired outcome cases / totally possible outcome cases
for chances we often transfer that number into a percentage by simply multiplying the number by 100.
to roll a die has 6 equally likely outcomes (1 - 6).
when we roll 2 dice, this has then 6×6 = 36 total outcomes (2 - 12), but their are not equally likely anymore, as different results of the individual dice can create the same sum result.
the first question (3 on the red die) deals with only one die (even though you role both dice)
the probability to get that 3 is
1/6
as there is only one desired case, and 6 possible outcomes.
anyway, the probability is
1/6 = 0.1666666666...
and the chance is
0.16666666666... × 100 = 16.67% (rounded to 2 decimals)
the second question (to get a total 5) is more interesting.
remember, we have 36 different possible results when rolling the dice.
how many are desired ? well, all that have a total of 5 points :
1 and 4
2 and 3
3 and 2
4 and 1
so, 4 cases.
the probabilty is then
4/36 = 1/9 = 0.111111111...
the chance for this is
0.111111111... × 100 = 11.11%
NOW, the big question is the probabilty of the combination of both events into one combined event.
remember : a 3 on the red OR a total of 5.
you see, there is an overlap between both events. that means they are not completely independent, because the red 3 is also a part of the cases to get a total of 5.
so, the complete answer is the same as the second detailed answer ("...or a red 3" does not create a new desired case) :
the probability is therefore
4/36 = 1/9 = 0.111111111...
the chance is
11.11%.