Question

Mary is going to paint a building that is 80 foot long, 23 feet wide, and 8 feet tall. Mary is trying to decide whether to use a five or seven inch brush. If the paint covers the surface in stroke and she can paint two foot strokes every minute, how many minutes would she save if she used the seven inch brush?

Answer 1

area of all the walls
\[A== 2wh+2lh=1648\]
width of brush be a, we get area covered per minute as
\[R=2*a\]
total time taken is
\[t=A/R=\frac{824}{a}\]
for a=5, we get time t5 = 164.8
for a=7, we get time t7 = 117.7143
so time saved is t=t5-t7=47.0847 minutes