A logistics operator investigated the maximum flight time of a commercial delivery drone fleet. The fleet consisted of three drone models: Scout, Carrier, and Heavy-Lift, with 120 Scout drones, 180 Carrier drones, and 300 Heavy-Lift drones.
She conducted flight tests individually with 20 drones. The maximum flight time (minutes) recorded during these tests are shown in Table 1.
Table 1 Maximum flight time (minutes) for each tested drone
| Drone | Flight Time (minutes) |
|---|---|
| 1 | 35 |
| 2 | 42 |
| 3 | 28 |
| 4 | 55 |
| 5 | 30 |
| 6 | 45 |
| 7 | 38 |
| 8 | 50 |
| 9 | 25 |
| 10 | 48 |
| 11 | 33 |
| 12 | 40 |
| 13 | 52 |
| 14 | 29 |
| 15 | 36 |
| 16 | 47 |
| 17 | 31 |
| 18 | 44 |
| 19 | 39 |
| 20 | 51 |
Explain how the sample of 20 drones could have been obtained from the three models in the fleet using stratified sampling.
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