What is the probability of drawing a k, q or j from a deck of playing cards?

Each of the four sets has a K, Q and J. 
That is 3 (each card) times 4 (for each suit) = 12
Each card deck is 52 cards.
The answer is 12/52 or 3/13

There are 4 type of cards for each King, Queen, or Jack, so that would be 12 cards over 52 total cards. Simplified would be 3/13.

Let the number be x.

First student increased the number by 23, therefore
⇒ x + 23

Second student decreased the number by 1, therefore
⇒ x - 1

The first student's result was 7 times greater than the result of the second student's, therefore
⇒ x + 23 = 7(x - 1)


Solve for x:

x + 23 = 7( x- 1)
x + 23 = 7x - 7
6x = 30
x = 5


The  number on the board is 5.