In how many ways 4 books can be chosen from 8 different books and be arranged in 4 spaces on a bookshelf?

hope this helps

Step-by-step explanation:

3*2 * 1 = 24 ways . It is called arrangement or permutations, while if you need to group some objects it is called combination and there we need to consider unique groups only.

10000

step-by-step explanation: divide by 2,

second option

step-by-step explanation:

the measures of a triangle equal 180. use that to find x.

2x+3x+4x=180

9x=180

9x/9=180/9

x=20

now you know x, you know angle a is 40°, angle b is 60°, angle c is 80°.

because angle a is 40°, the first option doesn't work.

because angle b is 60°, the second option does work.

when you add angle a and b, you get 100°. complementary means it equals 90°, so the third option doesn't work.

when you add angle a and c, you get 120°, which is not 100.