A bakery opened yesterday with its daily supply of 40 dozen rolls. Half of the rolls were sold by noon, and 80% of the remaining rolls were sold between noon and closing time. How many dozen rolls had been sold when the bakery closed yesterday?

Correct Answer: 4 dozen
Sold by noon = <math xmlns = "http://www.w3.org/1998/Math/MathML"><mfrac><mn>40</mn><mn>2</mn></mfrac><mo> = </mo><mn>20</mn><mo>&#xA0;</mo><mi>d</mi><mi>o</mi><mi>z</mi><mi>e</mi><mi>n</mi><mo>&#xA0;</mo><mi>r</mi><mi>o</mi><mi>l</mi><mi>l</mi><mi>s</mi></math>80% of remaining = <math xmlns = "http://www.w3.org/1998/Math/MathML"><mn>20</mn><mo>&#xD7;</mo><mn>80</mn><mo>%</mo><mo> = </mo><mn>16</mn><mo>&#xA0;</mo><mi>d</mi><mi>o</mi><mi>z</mi><mi>e</mi><mi>n</mi><mo>&#xA0;</mo><mi>r</mi><mi>o</mi><mi>l</mi><mi>l</mi><mi>s</mi></math> sold between noon & closing time<math xmlns = "http://www.w3.org/1998/Math/MathML"><mo>&#x2234;</mo></math> After closing <math xmlns = "http://www.w3.org/1998/Math/MathML"><mfenced><mrow><mn>20</mn><mo> - </mo><mn>16</mn></mrow></mfenced><mo>&#xA0;</mo><mi>d</mi><mi>o</mi><mi>z</mi><mi>e</mi><mi>n</mi><mo> = </mo><mn>4</mn><mo>&#xA0;</mo><mi>d</mi><mi>o</mi><mi>z</mi><mi>e</mi><mi>n</mi><mo>&#xA0;</mo><mi>r</mi><mi>o</mi><mi>l</mi><mi>l</mi><mi>s</mi><mo>&#xA0;</mo><mi>a</mi><mi>r</mi><mi>e</mi><mo>&#xA0;</mo><mi>u</mi><mi>n</mi><mi>s</mi><mi>o</mi><mi>l</mi><mi>d</mi><mo>.</mo></math>