Answer:
If the lifetime of batteries in the packet is 40.83 hours or more then, it exceeds for 5% of all packages.
Step-by-step explanation:
We are given the following information in the question:
Mean, μ = 15
Standard Deviation, σ = 1
Sample size = 4
Total lifetime of 4 batteries = 40 hours
We are given that the distribution of lifetime is a bell shaped distribution that is a normal distribution.
Formula:

Standard error due to sampling:

We have to find the value of x such that the probability is 0.05
P(X > x) = 0.05
Calculation the value from standard normal z table, we have,
Hence, if the lifetime of batteries in the packet is 40.83 hours or more then, it exceeds for 5% of all packages.
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Possible dimension of a box with a volume of 100 cubic cm
10 x 10 x 1 = 100
10 x 5 x 2 = 100
5 x 5 x 4 = 100
Surface area:
10 x 10 x 1 dimensions:
10 x 10 = 100 x 2 = 200 sq.cm
10 x 1 = 10 x 4 = 40 sq. cm
240 sq. cm * $0.05 / 100 sq.cm = $0.12 per box
0.12 per box * 100 boxes = $12
10 x 5 x 2 dimension
10 x 5 = 50 x 2 = 100 sq. cm
10 x 2 = 20 x 2 = 40 sq. cm
5 x 2 = 10 x 2 = 20 sq. cm
160 sq. cm * $0.05/100 sq. cm = $0. 08 per box
0.08 per box * 100 boxes = $8
5 x 5 x 4 dimension
5 x 5 = 25 x 2 = 50 sq. cm
5 x 4 = 20 x 4 = 80 sq. cm
130 sq. cm * $0.05/100 sq. cm = $0.065 per box
0.065 per box * 100 boxes = $6.50
The best dimension to use to have the least cost to make 100 boxes is 5 x 5 x 4. It only costs $6.50 to make 100 boxes.
Set up the equation like 4b+61=0, subtract 61 from both sides, and that'll be 4b=-61. Divide both sides by 4. b=15.25