Question

Helia began charging her cell phone battery when it was
30% charged. After 36 minutes, her cell phone battery
was 70% charged. If the cell phone battery charges at a
constant rate, how many more minutes will it take for
her cell phone battery to be exactly 80% charged?

Answer 1

Answer:

After 9 more minutes, her cell battery will be 80% charged.

Explanation:

Let us try to make an equation here to describe the relation between battery and time.

It is given that the battery charges at a constant rate so we can assume that

battery($b$) ∝ Time($t$)

$\Rightarrow b=kt$

But at t=0, the battery is already 30% charged so we rewrite the equation as follows:

$b=kt+30$           -(1)

Now,

at put t=36 and b=70 in Eqn 1:

We get    $k=\frac{10}{9}$

The final eqn is $b=\frac{10}{9}t +30$

Put b=80

We get:

$\Rightarrow80=\frac{10}{9} t+30\\\Rightarrow 50=\frac{10}{9}t\\\\\Rightarrow t=45 \text{min}$

∴ It will take (45-36)=9 more minutes to reach 80% battery.

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