Given the smaller cuboid has a surface area 400
cm^3
Let the dimensions be
5*x1*y1
Then the surface area is given
by:
SA = 2*5x + 2*5y + 2*xy =
400
==> 10x1 + 10y1 + 2x1y1 = 400
..............(1)
Now the larger
cuboid.
==> SA = 2*8x2 + 2*8y2 +
2*x2*y2
==> SA = 16x2 + 16y2 +
2x2y2..............(2)
But since both cuboids are similar ,
then we know that:
x1/x2 = 5/8==> x2= 8/5
x1
y1/y2 = 5/8 ==> y2 = 8/5
y1
Now we will substitute into
(2)
==> SA = 16(8/5)x1 + 16(8/5)y1 +
2(8/5)(8/5)x1y1
==> SA = (128/5)x1 + (128/5)y1 +
(128/25)x1y1
Now factor
128/5
==> SA = (128/5)*[ x1 + y1 +
(1/5)x1y1]
Now multiply and divide by
10.
==> SA = (128/10*5) [ 10x1+ 10y1 +
2x1y1]
But. from (1), we know that 10x1+10y1 + 2x1x2 =
400
==> SA = 128/50 * 400 =
1024
Then the surface area is 1024
cm^2
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