Answer: There are 97 nickels and 108 quarters.
Step-by-step explanation:
Let x = Number of nickels, y = Number of quarters.
As per given,
x+y = 205    ...(i)
0.05x+0.25y = 31.85 ... (ii)    [1 nickel = $0.05, 1 quarter = $ 0.25]
Multiply (ii) by 20, we get
x+5y=637   ...(iii)
Eliminate (i) from (iii)
4y = 432
⇒ y = 108   [Divide both sides by 4]
Put value of y in (i), we get

Hence, there are 97 nickels and 108 quarters.
 
        
             
        
        
        
Sounds like an id 10 t problem
        
             
        
        
        
(a) Average time to get to school
Average time (minutes) = Summation of the two means = mean time to walk to bus stop + mean time for the bust to get to school = 8+20 = 28 minutes
(b) Standard deviation of the whole trip to school
Standard deviation for the whole trip = Sqrt (Summation of variances)
Variance = Standard deviation ^2
Therefore,
Standard deviation for the whole trip = Sqrt (2^2+4^2) = Sqrt (20) = 4.47 minutes
(c) Probability that it will take more than 30 minutes to get to school
P(x>30) = 1-P(x=30)
Z(x=30) = (mean-30)/SD = (28-30)/4.47 ≈ -0.45
Now, P(x=30) = P(Z=-0.45) = 0.3264
Therefore,
P(X>30) = 1-P(X=30) = 1-0.3264 = 0.6736 = 67.36%
With actual average time to walk to the bus stop being 10 minutes;
(d) Average time to get to school
Actual average time to get to school = 10+20 = 30 minutes
(e) Standard deviation to get to school
Actual standard deviation = Previous standard deviation = 4.47 minutes. This is due to the fact that there are no changes with individual standard deviations.
(f) Probability that it will take more than 30 minutes to get to school
Z(x=30) = (mean - 30)/Sd = (30-30)/4.47 = 0/4.47 = 0
From Z table, P(x=30) = 0.5
And therefore, P(x>30) = 1- P(X=30) = 1- P(Z=0.0) = 1-0.5 = 0.5 = 50%