A park ranger uses two drones to observe wildlife. After letting the drones hover at the same height for a while, she decreases the height of the first drone by 38 3/4 feet in order to take pictures. She also decreases the height of the second drone, but only by 20% of the decrease in height of the first drone.

Question

Which THREE methods could be used to find the change in height, in feet, of the second drone?

A.
Multiply -38 3/4 by 1/5
B.
Multiply 38 3/4 by 1/10 then multiply by 1/2
C.
multiply by -38 by 0.2 then add 0.75
D.
Multiply
-38 3/4 by 1/5
E.
multiply -38.75 by 0.2

Answer 1

To find the change in height of the second drone, we need to calculate 20% of the decrease in height of the first drone. The first drone's decrease is 38 3/4 feet.

1. Convert 38 3/4 feet to an improper fraction or a decimal:

   • 38 3/4 = 38 + 3/4 = 38 + 0.75 = 38.75 feet.

2. Calculate 20% of 38.75 feet:

   • 20% = 0.2, so we want to calculate 0.2 * 38.75.

Now, let's evaluate the answer choices:

A. Multiply -38 3/4 by 1/5.

• This calculates 1/5 of the decrease, not 20% (which is 1/5 of 38.75).

B. Multiply 38 3/4 by 1/10 then multiply by 1/2.

• This calculates 1/10 of the decrease, then half of that, which is not 20%.

C. Multiply -38 by 0.2 then add 0.75.

• This is not a correct method since it incorrectly uses negative and adds to a whole number that doesn't represent our original decrease.

D. Multiply -38 3/4 by 1/5.

• Similar to choice A, this does not represent a 20% decrease.

E. Multiply -38.75 by 0.2.

• This correctly calculates 20% of the decrease in height of the first drone.

Thus, the valid method is:

E. multiply -38.75 by 0.2.

Recap of choices for the change in height of the second drone: Only option E correctly calculates 20% of the decrease of the first drone. The other options either misrepresent the desired calculation or are incorrect in their mathematical approach.