Since there is no repetition allowed, there are 10 possibilities for the 1st digit, 9 for the 2nd, 8 for the 3rd, and 7 for the 4th. This gives a total of (10)(9)(8)(7) = 5040 four-digit codes.
For all odd digits to be used, there are 5 possibilities for the 1st digit (1,3,5,7,9), 4 for the 2nd, 3 for the 3rd, 2 for the 4th. This gives a total of (5)(4)(3)(2) = 120 codes that only use odd digits.
Therefore there are 5040 - 120 = 4920 codes that do not consist of all odd digits. The probability is 4920/5040 = 41/42.
Easy, you just replace m with 2, and when a letter is placed next to a number then it means you multiply them, therefore
6*2-1=12-1 = 11
Since the slop of a line is positive, the graph of the line would begin to move upwards, rather than downwards. A graph line only moves downwards when the slope of the line is negative.