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The volume of a cube is equal to the volume of a cuboid whose length, breadth and height are in the ratio of 9:5:2. If the volume of the cube is 11,250 cm 3 , find the total surface area of the cuboid.
3780 cm 2
3430 cm 2
3650 cm 2
3520 cm 2 Question ID : 4410091703869 Option 1 ID : 4410096720569 Option 2 ID : 4410096720566 Option 3 ID : 4410096720568 Option 4 ID : 4410096720567 Status : Answered Chosen Option : C
3650 cm 2
Calculate the constant x3 from the volume product (9x├Ч5x├Ч2x=90x3=11250), then find x3=125, so x=5. Compute TSA using x=5 as 2(45x2+10x2+18x2)=2(73x2)=146├Ч25.
Volume of the cube = 11,250 cm┬│. Dimensions of the cuboid are in the ratio 9:5:2.
V=l├Чb├Чh,TSA=2(lb+bh+lh)
Calculate the constant x3 from the volume product (9x├Ч5x├Ч2x=90x3=11250), then find x3=125, so x=5. Compute TSA using x=5 as 2(45x2+10x2+18x2)=2(73x2)=146├Ч25.
Students often confuse the cube volume with the cuboid volume or fail to correctly solve for the common ratio variable x.
Set up cuboid dimensions
Let the length l=9x, breadth b=5x, and height h=2x. Given the volumes are equal, set VcuboidтАЛ=11250.
9x├Ч5x├Ч2x=11250
Solve for x
Simplify the volume equation to solve for x. We have 90x3=11250, so x3=9011250тАЛ=125.
x=3125тАЛ=5
Calculate cuboid dimensions
Using x=5, find the dimensions: l=9├Ч5=45 cm, b=5├Ч5=25 cm, and h=2├Ч5=10 cm.
l=45,b=25,h=10
Calculate Total Surface Area (TSA)
Apply the total surface area formula TSA=2(lb+bh+lh). Substituting the values: 2(45├Ч25+25├Ч10+45├Ч10).
TSA=2(1125+250+450)=2(1825)=3650
C is correct because the total surface area of the cuboid calculated using the dimensions 45, 25, and 10 cm is 3650 cm┬▓.
This concept of equating volumes is foundational for problems involving melting solids and recasting shapes, a frequent topic in competitive geometry.