Simple math.
Probability is equal to number of ways it can happen over number of total outcome
or
P = (n1 + n2 + n3 ...) / nTotal
So a coin has two sides so that means there only 2 possibility for that
While a cube has 6 possibility
The event will be done once.
You use the word and meaning that we should use multiplication to determine the number of total outcome
So
nTotal = 2 * 6
nTotal = 12
There are 3 even number in a cube (1, 3, and 5)
So it means we have to multiply 3 to number of ways in a coin which is 1
n1 = 3 * 1
n1 = 3
Lets now compute:
P = 3/12
P = 1/4
P = 0.25 or 25%
So it means there is a 25% probability that the coin will land tails up with an even number from the cube.
W can do this in list
Heads up(H)
-H1
-H2
-H3
-H4
-H5
-H6
Tails up(T)
-T1
-T2
-T3
-T4
-T5
-T6
A total of 12
Let's list the T with even number
-T1
-T3
-T5
We have 3
3/12 = 1/4 = 0.25 = 25%
I hope it helps.