Acandy bar is advertised as costing “three for $1.00” if jackie bought 21 andy bars at this price, how much money would she have saved if the price had been reduced to “seven for $2.00”?

This problem calls for calculating two different unit prices:

3 bars
= $0.33 (or $0.34) per bar; 21 bars would cost $6.93.
   $1

7 bars
= $0.35 per bar; 21 bars would cost $7.35
   $2

By purchasing the bars at the cheaper price Jackie could have saved

$7.35 - $6.93, or $0.42 (answer)