One student can paint a wall in 20 minutes. Another student can paint the same wall in 30 minutes. Working together, how long will it take for them to paint the wall?

10 minutes

12 minutes

15 minutes

25 minutes

1) in one minute for first wiil be 1/20

the other 1/30, it means that A paint in one minute 1/20 and B 1/30 then A+B in one minute 1/20 + 1/30 = 3+2/60 = 5 / 60, 5/60 = 1/12

if in one min they make 1/12 then in 12 min they paint all the wall