Question

After charging for 1/3 of an hour, a phone is at 2/5 of its full power. How long will it take the phone to charge completely

Answer 1

To find the total charging time for the phone, a proportion is used based on the given information. It will take 5/6 of an hour, or roughly 50 minutes, to fully charge the phone.

Step-by-step explanation:

If a phone has charged to 2/5 of its full power after 1/3 of an hour, we need to establish the rate at which the phone charges to predict how long it will take to reach full charge. We can set up a proportion since the charging rate is constant:

1/3 hour -> 2/5 of the phone's battery
Let x be the total time to charge the phone to full power.
Then, 1 hour -> 5/2 * 2/5 = 1 (full power)

So:

(1/3) / (2/5) = 1 / x
(x * 2/5) = 1/3
x = (1/3) / (2/5)
x = (1/3) * (5/2)
x = 5/6

Therefore, it will take 5/6 of an hour, or approximately 50 minutes, to charge the phone completely from zero to full power.

Answer 2

If 1/3 of an hour results in 2/5 of full power, double both. You are left with 2/3 of an hour resulting in 4/5% or 80% power. If 1/3 results in 2/5, divide both sides by two. The remaining 1/5 power will be gained in an additional 1/6 of an hour. 2/3 + 1/6 = 5/6 of an hour to gain full power