An air conditioner can coo the hall in 15 minutes while another takes 20 minutes to cool under similar conditions. if both air conditioners are switched on at same instance then how long will it take to cool the room?	Choose the correct choice from the following answers
A) about 5 minutes
B) about 7 minutes
C) about 15 minutes
D) about 19 minutes
E) about 9 minutes
Take LCM of 15 and 20 = 60   15*4= 
<gadget id="calculator">15*4</gadget>
<output>60</output>
60/ 20*3=60.   So if both are switched on together , room cooled in 60/(4+3)=60/7=8.57 minutes   8.57 can be round to 9 minutes , so about 9 minutes   ANSWabout 9 minutesR: about 9 minutes
<result>E</result>
An air conditioner can coo the hall in 15 minutes while another takes 20 minutes to cool under similar conditions. if both air conditioners are switched on at same instance then how long will it take to cool the room?