PSAT Math Grid-Ins Question 87: Answer and Explanation

Question: 87

The Kp Index measures the energy added to Earth's magnetic field from the Sun on a scale of 0–9, with 1 representing a solar calm and 5 or more indicating a magnetic storm, or solar flare. The magnetic fluctuations are measured in three-hour intervals (12 a.m.–3 a.m., 3 a.m.–6 a.m., and so on). The bar graph below shows the measurements for a five-day period in September.

Based on the graph, a solar flare lasted for how many hours on September 11?

Correct Answer: 15

Explanation:

15

Difficulty: Easy

Category: Tables and Graphs

Getting to the Answer: Read the graph carefully, including the key at the bottom that tells you that each bar represents a 3-hour period. The question tells you that a Kp Index of 5 or more indicates a solar flare. On September 11, the graph shows 4 bars at a Kp Index of 5 and 1 bar at a Kp Index of 6, for a total of five 3-hour periods during which a solar flare occurred. This represents a total of 5 × 3 = 15 hours. Grid in 15.