Answer: a) 683 b) 1067
Step-by-step explanation:
The confidence interval for population proportion is given by :-

a) Given : Significance level :
Critical value : 
Margin of error : 
Formula to calculate the sample size needed for interval estimate of population proportion :-

Hence, the required sample size would be 683 .
b) If no estimate of the sample proportion is available then the formula to calculate sample size will be :-

Hence, the required sample size would be 1067 .
Make the coefficient of y the same in both equations:
To do this, multiply equation one by 2, and equation two by 5 (this will make the coefficient 10 in both).
14x + 10y = 38
-35x - 10y = -80
Eliminate the y variable by adding the equations from each other
(14x + 10y = 38)
+ (-35x - 10y = -80)
= -21x + 0y = -42
We now have -21x = -42. The y variable has been eliminated.
Solve for x
-21x = -42
Divide both sides by -21 to get x on its own.
x = 2
Substitute x into the equation to find y.
7*2+5y=19
14+5y=19
Subtract 14 from both sides.
5y=19-14
5y=5
Divide by 5 on both sides to get y on its own.
y=5/5
y=1
The answer is (2,1)
-(-2x-6y=-16)
2x+6y=16
4x-6y=-58
Y's cancel out, then add the rest
6x=-42
divide both sides by six
x=-7
plug x into any previous equation
2(-7)+6y=16
-14+6y=16
6y=30
y=5