Question

A glider was 1400 feet above sea level. After the glider flew for 10 minutes, it had dropped to
4
5
of its earlier level. Which equation correctly shows one way to find the height of the glider after it dropped?


1400
−
1
5
(
1400
)
=
1120


1400
+
1
5
(
1400
)
=
1680


1400
−
4
5
(
1400
)
=
1120


1400
+
4
5
(
1400
)
=
1680

Answer 1

Answer: 1400 − 1/5(1400) = 1120.

Explanation: Dropping to 4/5 of the original means the glider lost 1/5 of 1400. So 1400 − (1/5 · 1400) = 1400 − 280 = 1120 (or directly 4/5 · 1400 = 1120).