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Answer 1 · 2016-11-30T14:01:50

60 books were donated.

What we are looking for is:

48 is 80% of what?

In mathematics "is" means " $=$ ".

"Percent" or "%" means "out of 100" or "per 100", Therefore 80% can be written as $80/100$ .

When dealing with percents the word "of" means "times" or "to multiply".

And we can call "what" $n$ .

So putting this altogether gives:

$48 = 80/100 *xx n$

Solving for $n$ gives:

$100/80 xx 48 = 100/80 xx 80/100 xx n$

$4800/80 = 8000/8000 x n$

$60 = n$

Answer 2 · 2016-11-30T14:08:59

The count of donated books was 60

The symbol % is a unite of measurement worth $1/100$

So 80% $-> 80/100$

Let the total count of books donated be $x$
Given that the count sold is 48
Given that the percentage sold is 80%

$80/100xx x = 48$

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If you multiply $80/100" by " 100/80$ you turn it into 1

So this is:

$80/100xx100/80 = (80xx100)/(100xx80) = (100xx80)/(100xx80) =100/100xx80/80 =1xx1$

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Multiply both sides by $100/80$

$1xxx= 4800/80 = 60$

$x=60$