The english alphabet has 26 letters.
A, B, C, .... X, Y, and Z.
and there are 10 digits,
1, 2, 3, 4, 5, 6, 7, 8, 9, and 0.
Now,
You can choose any of the 26 letters for the first character on the license plate.
Again any of the 26 letters for the second character, and for the third and the fourth, you can choose any of the 10 digits.
(Note: for both the case : alphabet and digits, repetitions are allowed)
Therefore,
Total number of licence plates
= 26 × 26 × 10 × 10 = 67600.
Hence,
There can be made 67,600 license plates.
2.
In a drawing of two black cards,
First draw is a black card
P(first card is black) = 26/52
= 1/2
Now, the selected card is not replaced, so in a next chance, there are only 25 cards are are available to choose a second black card, so
P(second Card is black) = 25/51
P(both black card) = 1/2 * 25/51
= 25/102