Find The Dimensions Of This Cuboid

Geometry Level 1

Find the sum of length, breadth & height of a cuboid whose whole surface area is 214 cm 2 , \text{cm}^2\negthickspace,\, with a base area of 42 cm 2 , \text{cm}^2\negthickspace,\, and with volume 210 cm 3 . \text{cm}^3\negthickspace.


The answer is 18.

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22 solutions

Leonardo Chandra
Dec 27, 2013

The whole surface: 2 ( l w + l h + w h ) = 214 2(lw+lh+wh)= 214

( l w + l h + w h ) = 107 (lw+lh+wh)= 107

42 + h ( l + w ) = 107 42+h(l+w)= 107

h ( l + w ) = 65 h(l+w)= 65

volume= 210

l w h = 210 lwh= 210

( 42 ) h = 210 (42)h= 210

h = 5 h= 5

5 ( l + w ) = 65 5(l+w)= 65

l + w = 13 l+w= 13

l = 13 w l= 13-w

l w = 42 lw= 42

( 13 w ) . w = 42 (13-w).w=42

w 2 13 w + 42 = 0 w^2-13w +42=0

( w 6 ) ( w 7 ) = 0 (w-6)(w-7)= 0

w = 6 w= 6 or w = 7 w=7

l = 13 w l= 13-w

l = 7 l= 7 or l = 6 l=6

So, the sums of length, width, and height is 6+7+5= 18

This is my opinion... Okay, you already know what is the sum of the length and width, and the value of the height, why don't you just add them up? This can save your time a little bit.

敬全 钟 - 7 years, 5 months ago

that's what you called a very long process but I understand

Jay Cyril Mijares - 7 years, 5 months ago

I have solved the same way but nice solution and representation !

Devesh Rai - 7 years, 5 months ago

easy way is lbh=210,lw=42,by solving these two we get h=5,which leaves lw=42 which must be 7*6 so l=7,b=6 so l+w+h=5+6+7=18

Lava Kumar Marati - 7 years, 2 months ago

length = L

breadth = B

height = H

area of base = B * H

42 = B * H         .........................(i)

volume = B * H * L

210 = (B * L) * H

210 = 42 * H [ from (i)]

 H = 5

surface area = 2(L B + B H + H*L)

  214  =  2(42 + 5B + 5L)

  5B + 5L + 42 = 107

  5(B + L) = 65

   B + L = 13

Therfore,

     H + B + L = 5 +13

                       =18

What happened to your LaTeX?

Victor Loh - 7 years, 5 months ago

this is how i solved

lakshya agrawal - 7 years, 3 months ago
Nicholas Wei
Jan 7, 2014

Let l represent the length, b represent the breadth and h represent the height of the cuboid.

Then we can derive the following equations based on the information provided.

1) lbh = 210

2) 2lb + 2lh + 2bh = 214

3) lb = 42

Afterwards, use simultaneous equations to find out the individual values of l,b and h. From equations 1 and 3, we can find h by this formula: h= lbh/lb = 210/42 = 5.

Then, from equation 2, we can simplify it to become lb + lh + bh =107, then substitute the value of h into the newly derived equation, which will become lb + 5l + 5b = 107.

Since lb = 42 from equation 3, we can safely conclude that 5l + 5b =107 -42 = 65.

Then factorize out the common factor 5 to get 5(l + b) = 65.

In the end, we should get l+b = 13. Then just add 13 to 5 to get 18, which is the sum of the lengths of the cuboid. Simple! :)

Saksham Agrawal
Dec 27, 2013

Let length = l Breadth=b Height=h. Total Surface area of a cuboid=2(lb+lh+bh). lb=42(given) So by substituting the value of lb in the equation of total surface area we get h(l+b)=65. We know lbh=Total volume=210(given) We know that h=65/(l+b). Therefore by subs. the value of h in volume formula we get l+b=13 therefore l+b+h=18.

can someone explain with diagram??

Amin Muhammad - 7 years, 5 months ago

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This is not that hard sorry

Simon Mos - 7 years, 3 months ago
Harshul Mathur
Dec 25, 2013

2(lb + bh+ hl) = 214 ...... (1) lb = 42 ........(2) lbh = 210 ....... (3)

using (2) & (3), h = 5 substituting the values in (1), we get l + b = 13 so, l+b+h = 13 + 5 = 18

Sagnik Ghosh
May 19, 2014

2(lb+bh+lh)=214 lb+bh+lh=214/2=107. Base area=lb=42. lb+bh+lh=107 bh+lh=107-42(lb=42) h(l+b)=65. Volume=lbh=210. volume/base area=lbh/lb=h h=210/42=5. h(l+b)=65 (l+b)5=65(h=5) l+b=65/5=13. l+b=13;h=5; l+b+h=13+5=18(Answer).

Vinay Kumar
May 13, 2014

assume: l-length b-breadth h-height given lbh=210...............Eq.1 lb=42....................Eq.2 2(lb+bh+hl)=214.....Eq.3

eq.2/eq.1implies h=5 substitute h=5 in eq.3 that implies 2(42+5(l+b))=214 (l+b)=13 l+b+h=13+5=18

Jason Vuong
May 4, 2014

xy = 42 & xyz = 210 ==> z = 5 2xy + 2xz + 2yz = 214 <=> 2(42) + 10x + 10y = 214 <=> x + y = 13 <=> (42/y) + y = 13 <=> y^2 - 13y + 42 = 0 <=> x = 6 or 7 ==>y = 42/6 or 42/7 = 7 or 6 So (x+y+z) = 6+7+5 = 18 or (x+y+z) = 7+6+5 = 18

I solved it indirectly... I take volume and divide it by base area. I get 5. So, H = 5. Then I split base area as 6 x 7. Which is value nearer to height value. So, I take 5, 6, 7 as l,b,h. So, l+b+h = 18 :)

Parth Vashisht
Mar 6, 2014

so simple man

Razi Ur Rehman
Feb 4, 2014

whole surface area 2(ab+bc+ca)=214 area of base ab=42 Volume abc=210 42.c=210 c=5 ab+bc+ca=107 42+5(a+b)=107 on solving a+b+13 a+b+c=13+5 =18

the surface area is given in the formula 2lw+2lh+2wh=214 (1) the base area is lxw=42 cm²(2) and the volume is lxwxh= 210 cm3 since the base is l x w we can now get the height by dividing the volume (210) by the area of the base(42) 210cm3/42cm²=5cm=h substitute h in eq.1 2lw+2lh+2wh=214 2lw+10l+10w=214(3) now tAke the value of w from the second eq. w=42/l substitute it in eq. (3) 2l(42/l)+10l+10(42/l)=214 84+10l+420/l=214l 10l²-130l+420=0 divide by common factor w/c is ten then factor l²-13l+42=0 (l-6)(l-7) l=7 w=6 h=5 add up and it's 18

we know, volume = area of base * height 210 = 42 * h

h = 5 cm

Now, Total Surface Area = 214

2(lb + bh + lh) = 214

Substituting h = 5,

2(lb + 5b + 5l) = 214

lb + 5b + 5l = 214/2 = 107

Since base area = length * breadth = 42,

Substituting the value of lb = 42,

42 + 5(b + l) = 107

5(l+b) = 107-42 = 65

l+b = 65/5 = 13

Now we have l+b = 13

Add h=5 on both sides,

l+b+h = 13+h = 13+5 = 18cm

Answer = 18 cm

Pankaj Garg
Jan 19, 2014

we have, 2(lb+bh+hl)=214 ........(1), l b h=210 ..............(2), l*b=42 ...(3) from (2) & (3) we get,
h=5.
put the value of h in ...(1). hence, we get (l+b)=13. so, l+b+h=18

Henry Okafor
Jan 17, 2014

Volume = b a s e a r e a × h e i g h t base area \times height . Height = 210 42 \frac{210}{42} = 5.

Surface area = 2(lb+lh+bh) = 214

lb+lh+bh = 107

But lb = 42... Therefore, lh+bh= 65.

But h = 5, therefore, 5(l+b)=65

l+b=13

Hence, l+b+h = 13+5 =18

April Jolongbayan
Jan 11, 2014

First, equate lxw=42 which is the base area, then The total surface area which is 214= 2(lw+wh+lh) and the third equation is the volume 210=lxwxh. L=42/w 214= 2(lw+wh+lh) 107=lw+wh+lh 107=42/w(w)+wh+42/w(h) 65=wh+42/w(h) H=65w/w2+42 210=42/w(w)( 65w/w2+42) W2-13w+42=0 W=6 or 7 L=6 or 7 H=5 W+h+l=18

Mridul Gupta
Jan 7, 2014

Let's say length, breadth and height are l,b,h resp. now, we have l b h=210 (volume of cuboid) l b =42 (base area of cuboid) substituting l b in above eq we get h=5; now total surface area of a cuboid is 2 (l b+b h+h l) = 214 (given) soving and subs known values we get sum =18

Prasun Biswas
Dec 28, 2013

Let the length, breadth and height of the cuboid be l , b , h l,b,h respectively. We know that Area of Base = l b =lb , Volume of the cuboid = l b h =lbh and Total Surface Area of Cuboid = 2 ( l b + b h + l h ) =2(lb+bh+lh) .

GIven that, l b = 42... ( i ) lb=42 ...(i) and l b h = 210.... ( i i ) lbh=210 ....(ii)

Dividing (ii) by (i), we get, l b h l b = 210 42 h = 5 \frac{lbh}{lb}=\frac{210}{42} \implies h=\boxed{5}

So now we have the height, h=5 cm. Now, we have ---

2 ( l b + b h + l h ) = 214 2(lb+bh+lh)=214

2 ( l b + h ( l + b ) ) = 214 \implies 2(lb+h(l+b))=214

2 ( 42 + 5 ( l + b ) ) = 214 84 + 10 ( l + b ) = 214 10 ( l + b ) = 130 l + b = 13 \implies 2(42+5(l+b))=214 \implies 84+10(l+b)=214 \implies 10(l+b)=130 \implies l+b=\boxed{13}

So, Sum of l , b , h = l + b + h = ( l + b ) + h = 13 + 5 = 18 l,b,h = l+b+h = (l+b)+h = 13+5 = \boxed{18} cm

Jatin Valecha
Dec 27, 2013

l,b,h.. 7,6,5 .... 18 do math

and one more way .. lbh=210 and lb+bh+lh=214 ....... eq2/eq1 ... also leads same

JATIN VALECHA - 7 years, 5 months ago
Bazil Ali
Dec 27, 2013

Let a,b and c be the length,breadth and height.

Its given ab=42 and abc=210, so c=5

Also given that 2(ab+bc+ca)=214

i.e ab+bc+ca=107

c(b+a)=65,since ab=42

a+b=13,c=5

So a+b+c=18

Abhik Paul
Dec 27, 2013

Let a,b,h be the length, breadth and height of the cuboid respectively. Thus from given Total surface area, 2(ab+bh+ha)=214 Base area, ab=42 Volume, abh=210

Solving we get, h=5 and a+b=13

thus, the required answer is 18

Abu Asif
Dec 25, 2013

2 ( l x b ) + 2 ( h x b) + 2 ( l x h) = 214SqCm l x b = 42 SqCm & l x b x h= 210CuCm

Now the solution

42x h = 210 --- h = 210/42= 5Cm

2 x 42 + 2 x 5 b + 2 x 5 x l =214 10(l + b ) = 214- 84= 130 ( l + b ) = 13

Hence l +b+h= 13+5 = 18Cm

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