a, band c can do a piece of work in 11 days, 20 days and 20 days respectively, working alone. how soon can the work be done if a is assisted by band c on alternate days?  Select the correct option:
A) 7 days
B) 8 days
C) 9 days
D) 10 days
E) 11 days
<gadget id="calculator">20 / 11</gadget>
<output>20/11 = around 1.818182</output>

<gadget id="calculator">20 / 20</gadget>
<output>1</output>

<gadget id="calculator">(20/11) + 1</gadget>
<output>31/11 = around 2.818182</output>

<gadget id="calculator">(31/11) + (31/11)</gadget>
<output>62/11 = around 5.636364</output>

<gadget id="calculator">(62/11) / 2</gadget>
<output>31/11 = around 2.818182</output>

<gadget id="calculator">20 / (31/11)</gadget>
<output>220/31 = around 7.096774</output>

<result>A</result>
a, band c can do a piece of work in 11 days, 20 days and 20 days respectively, working alone. how soon can the work be done if a is assisted by band c on alternate days?
divide(20, divide(add(add(divide(20, 11), divide(20, 20)), add(divide(20, 11), divide(20, 20))), const_2))
"( a + b ) ' s 1 day ' s work = 1 / 11 + 1 / 20 = 31 / 220 ( a + c ) ' s 1 day ' s work = 1 / 11 + 1 / 20 = 31 / 220 work done in 2 day ' s = 31 / 220 + 31 / 220 = 31 / 110 31 / 110 th work done in 2 days work done = 110 / 31 * 2 = 7 days ( approx ) answer : a"