at the rate of 4 peaches for a half dollar , 20 peaches will cost

An alternate and more algebraic approach is to take the fact and 4 peaches=.50 dollars and make a proportion.  It would look like

$x/20 peaches=$0.50/4 peaches

Multiply both sides by 20 to solve for x

x=20(.5)/4=5(.5)=2.5

Lets start at the base and work our wau up.

We know 4 peaches costs half a dollar

That means 8 peaches would be one whole dollar

add four more peaches and we see that 12 peaches costs $1.50

This means 16 peaches would add another half dollar so now we are at $2.00

Adding four more adds another half dollar so 20 peahces costs $2.50, a strikingly good deal!