To find the change in height of the second drone, we first need to determine the decrease in height of the first drone, which is \( 38 \frac{3}{4} \) feet. The second drone's height is decreased by 20% of that decrease.
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Convert \( 38 \frac{3}{4} \) feet into an improper fraction:
\( 38 \frac{3}{4} = \frac{38 \times 4 + 3}{4} = \frac{152 + 3}{4} = \frac{155}{4} \). -
Calculate 20% of this value:
To find 20%, you multiply by 0.2 (or \( \frac{1}{5} \)): \[ \text{Decrease in height of the second drone} = 0.2 \times \frac{155}{4} = \frac{155}{4} \times \frac{1}{5} = \frac{155}{20}. \]
This can also be calculated in decimal form: \[ 20% = 0.2 \quad \Rightarrow \quad 38.75 \cdot 0.2 = 7.75 \text{ feet.} \]
Now, let's evaluate the options:
A. Multiply -\( 38 \frac{3}{4} \) by \( \frac{1}{5} \)
- Incorrect (this gives 20% of the negative value, but we need the change in positive, so not useful here).
B. Multiply \( 38 \frac{3}{4} \) by \( \frac{1}{10} \) then multiply by \( \frac{1}{2} \)
- Incorrect (this approach would calculate \( 5% \), not \( 20% \)).
C. Multiply -38 by 0.2 then add 0.75
- Incorrect (this does not correctly calculate the height decrease).
D. Multiply -\( 38 \frac{3}{4} \) by \( \frac{1}{5} \)
- Incorrect (similar reasoning to A).
E. Multiply -\( 38.75 \) by 0.2
- Correct (this gives the decrease directly as \( -7.75 \) when intended for the second drone, which is the right approach).
Thus, the correct method is E. However, if all answers are strictly about finding the actual positive change without negatives, none of the methods presented would be correctly combining the steps needed accurately to indicate both the correct aspect of decrease and applicability here.
Therefore, out of these, E is the only viable calculation method presented.
2 answers