Squares are cut from each corner of a 0.5m xx 0.5m0.5m×0.5m square of cardboard and the sides folded up to make an open box. What is the maximum possible volume of the box?

1 Answer
May 29, 2015

Consider the general case of a square sheet of cardboard with sides of length ss and square cut outs at each corner with side tt.

The area of the bottom of the resulting box will be (s-2t)^2(s2t)2.
The height of the box will be tt.
The volume of the box will be area xx height = (s-2t)^2*tarea×height=(s2t)2t

(s-2t)^2*t = (s^2-4st+4t^2)*t(s2t)2t=(s24st+4t2)t

= 4t^3-4st^2+s^2t=4t34st2+s2t

The maximum of this will occur at some point where the derivative is zero...

0 = d/(dt)(4t^3-4st^2+s^2t) = 12t^2-8st+s^20=ddt(4t34st2+s2t)=12t28st+s2

=12t^2-6st-2st+s^2=12t26st2st+s2

=(12t^2-6st)-(2st-s^2)=(12t26st)(2sts2)

=6t(2t-s)-s(2t-s)=6t(2ts)s(2ts)

=(6t-s)(2t-s)=(6ts)(2ts)

So t=s/6t=s6 or t=s/2t=s2

If t=s/2t=s2 the volume is 00 because (s-2t) = 0(s2t)=0

So the maximum volume occurs when t=s/6t=s6.

Then

volume = (s-2t)^2*tvolume=(s2t)2t

= (s-2(s/6))^2*s/6=(s2(s6))2s6

=((2s)/3)^2*s/6=(2s3)2s6

=4/54s^3=454s3

=2/27s^3=227s3

If s=0.5ms=0.5m

s^3 = 0.125m^3s3=0.125m3

and

2/27s^3 = 1/108m^3 = 0.00dot(9)2dot(5)m^3 = 9259.dot(2)5dot(9)cm^3227s3=1108m3=0.00.92.5m3=9259..25.9cm3