Answer:
To completely fill the sandbox will cost $56
Step-by-step explanation:
First, we calculate volume of the rectangular-shaped sandbox:

We know that density of sand is 100 pounds per cubic foot. Then, to fill the sand box that has a volume of 8 cubic foot, we calculate by rule 3:
1cubic foot..............100 pounds
8 cubic foot.............x pounds


We will need 800 pounds of sand to fill the sandbox, then we can calculate by rule 3 the number of bags needed and next the total cost of them:
50 pounds.......1bag
800 pounds.....x bags

To calculate the cost:
1 bag ..................$3.50
16 bags.................$x

To completely fill the sandbox will cost $56
Calculate for the mean/ average of the given numbers:
μ = (1 + 2 + 3 + 4 + 5) / 5 = 3
Then, we calculate for the summation of the squares of differences of these numbers from the mean, S
S = (1 - 3)² + (2 - 3)² + (3 - 3)² + (4 - 3)² + (5 - 3)²
S = 10
Divide this summation by the number of items and take the square root of the result to get the standard deviation.
SD = sqrt (10 / 5) = sqrt 2
SD = 1.41
Thus, the standard deviation of the given is equal to 1.41.