Algebra

Okay from the question, 

5 members can paint wall in = 27 min

 

∴ By inverse proportion, 

18 members can paint wall in \(={27 *5 \over 18}\)

                                                = 7 min and 30 sec

These question still make me thinkg

I do them a bit at a time.

 

5 people take 27 minutes

so one person must take 27*5=135 minutes

so 18 people will take 135 divided by 18 = 7.5minutes

= 7 minutes 30 sec   just as answer guest said.