A drilling machine can drill 12 holes in 6 minutes. If the machine drills holes at a constant speed, it can drill ______ holes in 25 minutes.

I find an easy way to answer questions like this is by 'dimensional analysis'....

Dimensions   mins/holes     and mins

 

mins  /  (mins/holes)   = holes     (because 'mins' cancel out)

 

25 mins   /   (6 mins/12 holes)  = 300/6 holes = 50 holes

50

two holes every one minute