two pipes a and b can fill a tank in 36 hours and 45 hours respectively. if both the pipes are opened simultaneously, how much time will be taken to fill the tank? Select the correct option:
A) 20 hrs	B) 22 hrs	C) 23 hrs	D) 24 hrs	E) 21 hrs
<gadget id="calculator">1 / 36</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">1 / 45</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">(1/36) + (1/45)</gadget>
<output>1/20 = around 0.05</output>

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

<result>A</result>
two pipes a and b can fill a tank in 36 hours and 45 hours respectively. if both the pipes are opened simultaneously, how much time will be taken to fill the tank?
divide(const_1, add(divide(const_1, 36), divide(const_1, 45)))
"1 / ( 1 / 36 + 1 / 45 ) = 180 / 9 = 20 hrs answer : a"