It is 10x4x3x2 equals two hundred and forty
Let's first break it down to the time 8 people need for one wall. That would be 10 minutes, right? If one person would have to do it in stead of 8, you'd expect him to take 80 minutes.
To paint 7 walls, he would nee 7x80 = 560 minutes. 10 people would do that 10 times faster, ie., 56 minutes.
I know puzzles like these always have a mindtrick. Did I miss anything?? ;-)
General term of a geometric sequence is
a(n)=a(1)×r^(n-1)
a1=5
a2=5×6=30
a3=5×6²=180
a4=5×6³=1080
