Mary and dan went to a bookstore. mary bought 2 notebooks and 3 pens for $14.50. dan bought 1 notebook and 2 pens for $7.50. how much does one notebook cost?

Let be the cost, respectively, of a notebook and a pen. If you buy 2 notebooks and 3 pens (which we know is a cost of $14.50), you spend

Similarly, if you buy 1 notebook and 2 pens (which we know is a cost of $7.50), you spend

These two equations form the following system:

Multiply the second equation by 2:

Subtract the first equation from the second:

So, a pen costs 0.5 dollars. Plug this equation in the second equation:

answer set (b) 0.5, 3/4 80% is in order from least to greatest.  

step-by-step explanation:

in order to compare rational numbers to each other, it is much easier if they are in the same form.   typically, the best form in which to evaluate rational numbers is in decimals.   in order to convert a percent to a decimal, you would divide the given percentage by 100.   you can also accomplish the conversion by moving the decimal point over two places to the left.   for example, the decimal value of 80% is 80/100, or 0.8.   in order to convert a fraction to a decimal, you need to divide the numerator by the denominator.   for example, 3/4 is 0.75.   so, for choice (b) 0.5 3/4 (0.75), 80% (0.8) is the only choice in which the numbers are in order from least to greatest.