Answer:
Step-by-step explanation:
this is a set problem (mathematical set) 
30 students played soccer
9 students played cricket and soccer
x students played neither cricket nor soccer
3x students played cricket only.
we can see that in the first set 21 appears and in the middle of the set 9 because it says 30 students played soccer adding x and 3x we have the following formula
30 + x + 3x = 50 where x is equal to 5 then ask us Determine the number of students who played cricket. then the value would be 3x + 9 = (3x5) + 9 = 24
 
        
             
        
        
        
Answer: Light waves
Step-by-step explanation:
Used in the usual sense, radiant energy is just light. When you turn on your electric stove unit, it heats up and emits radio waves, infrared waves, and visible light waves. All of these waves are just light with different frequencies.
 
        
                    
             
        
        
        
Answer:
The minimum sample size needed for use of the normal approximation is 50.
Step-by-step explanation:
Suitability of the normal distribution:
In a binomial distribution with parameters n and p, the normal approximation is suitable is:
np >= 5
n(1-p) >= 5
In this question, we have that:
p = 0.9
Since p > 0.5, it means that np > n(1-p). So we have that:





The minimum sample size needed for use of the normal approximation is 50.