Curious Cuboid

Geometry Level 1

The diagram above shows a rectangular prism. Given that the surface area of surface A A , B B , and C C are 1024, 81 and 49 respectively, find the volume of the cuboid.


The answer is 2016.

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8 solutions

Rishabh Jain
Feb 3, 2016

Let the edge lengths of the cuboid be a,b,c
Given:ab=1024.....(1)
bc=81....(2)
ca=49.....(3)
Multiplying these equations we get: ( a b c ) 2 = 1024 × 81 × 49 = 201 6 2 (abc)^2=1024\times81\times 49=2016^2 a b c = 2016 \Rightarrow abc=\large {2016}
And since the volume V=abc , 2016 \Large\boxed{2016} is the required answer.


Very helpful

Kishore Ilayaraja - 11 months ago

let L , W L,W and H H be the length, width and height of the rectangular prism respectively

then, we have

H L = 81 HL=81 ( 1 ) \color{#D61F06}(1)

H W = 49 HW=49 ( 2 ) \color{#D61F06}(2)

L W = 1024 LW=1024 ( 3 ) \color{#D61F06}(3)

from ( 1 ) \color{#D61F06}(1) , H = 81 L H=\dfrac{81}{L} , substitute this in ( 2 ) \color{#D61F06}(2) , we have

81 L W = 49 \dfrac{81}{L}W=49 or W = 49 81 L W=\dfrac{49}{81}L , substitute this in ( 3 ) \color{#D61F06}(3) , we have

L 2 ( 49 81 ) = 1024 L^2 \left(\dfrac{49}{81}\right)=1024 \color{#3D99F6}\large\implies L = 288 7 L=\dfrac{288}{7}

solving for H H , we get

H = 81 288 7 = 63 32 H=\dfrac{81}{\frac{288}{7}}=\dfrac{63}{32}

solving for W W , we get

W = 49 81 × 288 7 = 224 9 W=\dfrac{49}{81} \times \dfrac{288}{7}=\dfrac{224}{9}

Finally, the volume is

V = L W H = 288 7 × 224 9 × 63 32 = V=LWH=\dfrac{288}{7} \times \dfrac{224}{9} \times \dfrac{63}{32}= 2016 \boxed{\large2016}

Akash Sharma
Feb 5, 2016

Let side of the cuboid be x,y,z given Xy=1024... (1) Yz=81.... (2) Za=49...(3) Multiply eq. 1,2,3... We get (XYZ)^2=(32X9X7)^2 XYZ=2016 Hence volume of cuboid is 2016

Let x x be the height, y y be the length and z z be the width of the cuboid. Then we have, z y = 1024 , x y = 81 zy=1024,xy=81 and x z = 49 xz=49 . We know that the volume is x y z xyz , so we have

( z y ) ( x y ) ( x z ) = 1024 ( 81 ) ( 49 ) (zy)(xy)(xz)=1024(81)(49)

z 2 y 2 x 2 = 4064256 z^2y^2x^2=4064256

z 2 y 2 x 2 = 4064256 \sqrt{z^2y^2x^2}=\sqrt{4064256}

x y z = 2016 cubic units xyz=\boxed{2016~\text{cubic units}}

Oli Hohman
Jun 12, 2016

If you label the picture with L=length, W=width, and H=height, then the volume of a cuboid is V= L W H. The surface area of A = 1024 = L W (according to my diagram). The surface area of B = 81 = W H and the surface area of C = 49 = L H. Substituting 1024 for L W in the volume equation yields V = 1024*H.

If we compare the surface area equations of B and C by dividing the two, you have

81/49 = (W H)/(L H) = W/L (9/7)^2 L = W

Plugging W in terms of L back into the surface area of A equation, you get L (9/7)^2 L = 1024 Solving for L gives L = 224/9

Plugging back into the surface area of A equation will give you W, too. Solving for W gives W = 288/7.

You can use the surface area equation of B or C for the rest of the problem.

81/W = H, so 81/(288/7) = 63/32 = H

Volume of Cuboid = L W H = (224/9)(288/7)(63/32) = 2016

Moderator note:

Great! Thanks for verifying that there are valid dimensions such that the geometrical object could exist. That is often ignored when the answer is obtained algebraically (and sometimes the geometrical object doesn't exist).

Umesh S M .
Jun 1, 2021

Given A= 1024. B =81, C=49 all the above are squares of 32, 9 and 7 respectively and in the cuboid is having the square surfaces . so the volume of the cuboid is l x b x h= 32 x 9 x 7 = 2016

Marvin Kalngan
May 8, 2020

Volume = 102 4 2 + 8 1 2 + 4 9 2 = 2016 cubic units \text{Volume}=\sqrt{1024^2+81^2+49^2}=\boxed{\text{2016 cubic units}}

Nirmit Bhanderi
Apr 6, 2019

given :- ab = 1024 ------(1) bc = 81 ----------(2) ac = 49 ----------(3)

Multiplying these equations :- (1) (2) (3)

(abc)^2 = 1024 * 81 * 49

abc = square root of 1024 * 81 * 49

Volume = 2016

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