Answer:
questions 2 answe is x+3less than equal to 13
 
        
             
        
        
        
Answer:
20%
Step-by-step explanation:
21/ 105
= 0.2 x 100
20%
 
        
                    
             
        
        
        
Cos(68)=z/24
Z=24cos(68)
Find the answer by the calculator 
Second question,
Cos(x)=16/34
X=cos^-1(16/34)
Use calculator
        
             
        
        
        
A
Because i did the math and i had this question before
 
        
             
        
        
        
The number of mole of pure 11C (carbon-11) initially present is 0.2727 mole
<h3>Description of mole </h3>
The mole of a substance is related to it's mass and molar mass according to the following equation 
Mole = mass / molar mass 
With the above formula, we can obtain the number of mole of pure 11C. Detail below:
<h3>How to determine the mole of 11C</h3>
From the question given, the following data were obtained:
- Molar mass of 11C = 11 g/mol
- Mass of 11C = 3 g
- Mole of 11C =?
Mole = mass / molar mass 
Mole = 3 / 11
Mole = 0.2727 mole
Therefore, the number of mole of pure 11C initially present is 0.2727 mole
Learn more about mole:
brainly.com/question/13314627
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