Question 632370
if 2 1/2 cost $20, how much do 3 1/2 cost?
<pre>
This one is more easily with decimals. Use 1/2 as .5
Consider the problem this way:

if 2.5 cost $20, how much do 3.5 cost?

2.5 is to $20 as x is to 3.5

{{{2.5/20}}} = {{{3.5/x}}}

Cross-multiply:

(2.5)(x) = (20)(3.5)
    2.5x = 70
    {{{2.5x/2.5}}} = {{{70/2.5}}}
       x = $28

Edwin</pre>