Final answer:
The correct dimensions for Mr. Johnston's new rectangular garden are a length of 25 feet and a width of 10 feet, based on the given perimeter of 70 feet. The options provided in the question do not include these dimensions, suggesting a discrepancy in the question or the answers provided.
Step-by-step explanation:
Let's take a systematic approach to solve Mr. Johnston's garden redesign. Given that the perimeter of the new rectangular garden is 70 feet and the length (L) is 5 feet shorter than three times the width (W), we can write two equations based on the properties of rectangles:
- L = 3W - 5
- The perimeter P of a rectangle is given by P = 2L + 2W, so 70 = 2(3W - 5) + 2W
We can solve for W in the second equation:
70 = 2(3W - 5) + 2W
70 = 6W - 10 + 2W
70 = 8W - 10
80 = 8W
W = 10
Now that we know the width, we can find the length:
L = 3(10) - 5 = 30 - 5 = 25
Thus, the dimensions of the new garden are:
- Length: 25 feet
- Width: 10 feet
The correct answer is not listed among the options provided, indicating a possible mistake in the question or the answer choices.