Answer:
22 2/9
Step-by-step explanation:
When z "varies jointly" with x and y, it can be described by the formula
z = kxy
Here, we have bags of mulch (n) varying jointly with area (a) and depth (d), both in feet. The given information can let us find the value of k.
n = kad
10 = k·(120)(1/4)
10/30 = k = 1/3 . . . . . divide by the coefficient of k
Now, we can fill in the other values of interest.
n = (1/3)·(200)·(1/3) = 200/9
n = 22 2/9
You need 22 2/9 bags of mulch to cover 200 ft² to a depth of 4 inches.
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Comment on the problem
This problem requires the formula be written with both area and depth expressed in feet, yet it gives depth in inches. The formula can also be written using depth in inches. In that case, k = 1/36.
