11
(9, 18, 27, 36, 45, 54, 63, 72, 81, 90 and 99)
Those numbers divisible by 9 are the multiple of 9; thus need to know how many multiples of 9 there are between 1 and 100:
100 ÷ 9 = 11 r 1 ÷ last multiple of 9 is 11 × 9 (= 99)
→ There are 11 - 1 + 1 = 11 numbers between 1 and 100 which are divisible by 9.
(They are 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99.)
To solve this problem you must apply the proccedure shown below:
1- You have that the laddder makes an angle of
with the ground and the top of the ladder reaches
.
2- Therefore, you have:

Where:

3-You must substitute values and solve for the lenght, as following:

Therefore, the answer is: 
Step-by-step explanation:
there are
150 + 83 + 57 + 10 = 300 students in total.
so,
100% = 300
1% = 100%/100 = 300/100 = 3
a.
150 / 3 = 50%
b.
83 / 3 = 27 2/3 % or 27.66666...%
c.
57 / 3 = 19%
d.
10 / 3 = 3 1/3 % or 3.333333...%