Question

lin uses an app to graph the charge on her phone.

1. when did she start using her phone?
2. when did she start charging her phone?
3. while she was using her phone, at what rate was lin’s phone battery dying?

Explanation:

Sub - question 1:

Step1: Analyze the graph trend

The battery percentage starts to decrease at 2 hours after noon, which means she started using her phone (causing battery to drain) at that time.

Step1: Analyze the graph trend

The battery percentage starts to increase at 8 hours after noon, which means she started charging her phone (causing battery to rise) at that time.

Step1: Identify the time and battery change

From 2 hours after noon to 4 hours after noon, the time elapsed is \(4 - 2=2\) hours. The battery percentage changed from 100% to 40%, so the change in battery percentage is \(100 - 40 = 60\) percentage points.

Step2: Calculate the rate

The rate of battery draining is the change in battery percentage divided by the time elapsed. So the rate \(r=\frac{60}{2}=30\) percentage points per hour.

Answer:

She started using her phone 2 hours after noon (or 2:00 PM).

Sub - question 2: