Pipes A and B can fill a cistern in 6 and 30 minutes respectively. They are opened an alternate minutes. Find how many minutes, the cistern shall be full? Choose one:
A) 13
B) 10
C) 16
D) 18
E) 19
:   1/6 + 1/30 = 1/5   5 * 2= 
<gadget id="calculator">5 * 2</gadget>
<output>10</output>
10.Answer:10
<result>B</result>
Pipes A and B can fill a cistern in 6 and 30 minutes respectively. They are opened an alternate minutes. Find how many minutes, the cistern shall be full?