Lets say the 3x3 Matrix is
M = [1 5 2 ]
[1 1 7 ]
[0 -3 7 ]
We apply the Gauss-Jordan elimination method
(Procedure and result shown in the image below)
For option a, y = 3(4) - 1 = 12 - 1 = 11 [not correct]
For option b, y = 3(2) - 1 = 6 - 1 = 5 [correct]
Therefore option b is a solution to the given equation.
Answer:
1 in 10, or 10% because there is a 90% chance she will choose the wrong number.
This means that you have to divide 3 by 3/4. So, let's just do that
3 divided by 3/4
3 times 4/3
4
So, Cindy would be able to solve 4 puzzles in 3 hours.
Hope this helps :D