First you have all ten books, but then every time after, you loose one because you can't put the same book in the group twice.
10 * 9 * 8 * 7 = 5040 groups
Step-by-step explanation:
If you have any questions about the way I solved it, don't hesitate to ask me in the comments below :)
Answer:
A. 4.8°
Step-by-step explanation:
We have that,
The horizontal distance for the ramp = 12 feet.
Maximum height of the ramp = 1 feet.
So, we get that the value of the angle 'x' made by the ramp with the ground is given by,

i.e. 
i.e. 
i.e. 
i.e. x = 4.8°
Thus, the maximum angle made by the ramp with the ground is 4.8°.