Answer:
a.1.90 years
Step-by-step explanation:
We have that to find our 
level, that is the subtraction of 1 by the confidence interval divided by 2. So:
Now, we have to find z in the Ztable as such z has a pvalue of 
.
So it is z with a pvalue of 
, so 
Now, find the margin of error M as such
In which 
is the standard deviation of the population and n is the size of the sample.
In this question:
So
So the correct answer is:
a.1.90 years
1800 ft² = 3 pounds
[divide by 3 through]
1800 ÷ 3 = 3 ÷ 3
600ft² = 1 pound
[8400 ÷ 600 = 14; so multiply by 14 through]
600 x 14 = 1 x 14
8400ft² = 14 pounds
we need 14 pounds to cover 8400 square feet.
[Find number of 4 pounds bags needed]
14 ÷ 4 = 3.5
So we need to use 4 bags of 14 pounds of lawn seeds.
80%=.8, .8*685=548. This is the simple math that you need. For the percentages, move the decimal place two places to the left and then multiply by the number that you want to get the percentage of.
