Try this beautiful problem from AMC 10A, 2004 based on Mensuration: Cylinder
Problem on Cylinder - AMC-10A, 2004- Problem 11
A company sells peanut butter in cylindrical jars. Marketing research suggests that using wider jars will increase sales. If the diameter of the jars is increased by \(25\%\) without altering the volume, by what percent must the height be decreased?
\(16\)
\(18\)
\(20\)
\(36\)
\(25\)
Key Concepts
Mensuration
Cylinder
Percentage
Check the Answer
Answer: \(36\)
AMC-10A (2004) Problem 11
Pre College Mathematics
Try with Hints
Let the radius of the jar be \(x\) and height be \(h\).then the volume (V) of the jar be\(V\)= \(\pi (x)^2 h\). Diameter of the jar increase \(25 \)% Therefore new radius will be \(x +\frac{x}{4}=\frac{5x}{4}\) .Now the given condition is "after increase the volume remain unchange".Let new height will be \(h_1\).Can you find out the new height....?
can you finish the problem........
Let new height will be \(H\).Therefore the volume will be \(\pi (\frac{5x}{4})^2 H\).Since Volume remain unchange......
Area of Rectangle Problem | AMC 8, 2004 | Problem 24
Try this beautiful problem from Geometry from AMC-8, 2004 ,Problem-24, based on area of Rectangle.
Rectangle | AMC-8, 2004 | Problem 24
In the figure ABCD is a rectangle and EFGH is a parallelogram. Using the measurements given in the figure, what is the length d of the segment that is perpendicular to HE and FG?
$7.1$
$7.6$
$7.8$
Key Concepts
Geometry
Rectangle
Parallelogram
Check the Answer
Answer:$7.6$
AMC-8, 2004 problem 24
Pre College Mathematics
Try with Hints
Find Area of the Rectangle and area of the Triangles i.e \((\triangle AHE ,\triangle EBF , \triangle FCG , \triangle DHG) \)
Can you now finish the problem ..........
Area of the Parallelogram EFGH=Area Of Rectangle ABCD-Area of\((\triangle AHE +\triangle EBF + \triangle FCG + \triangle DHG) \)
can you finish the problem........
Area of the Rectangle =\(CD \times AD \)=\(10 \times 8\)=80 sq.unit
Area of the \(\triangle AHE\) =\(\frac{1}{2} \times AH \times AE \)= \(\frac{1}{2} \times 4 \times 3\) =6 sq.unit
Area of the \(\triangle EBF\) =\(\frac{1}{2} \times EB \times BE \)= \(\frac{1}{2} \times 6 \times 5\) =15 sq.unit
Area of the \(\triangle FCG\) =\(\frac{1}{2} \times GC \times FC\)= \(\frac{1}{2} \times 4\times 3\) =6 sq.unit
Area of the \(\triangle DHG\) =\(\frac{1}{2} \times DG \times DH \)= \(\frac{1}{2} \times 6 \times 5\) =15 sq.unit
Area of the Parallelogram EFGH=Area Of Rectangle ABCD-Area of\((\triangle AHE +\triangle EBF + \triangle FCG + \triangle DHG) \)=\(80-(6+15+6+15)=80-42=38\)
As ABCD is a Rectangle ,\(\triangle GCF\) is a Right-angle triangle,
Therefore GF=\(\sqrt{4^2 + 3^2}\)=5 sq.unit
Now Area of the parallelogram EFGH=\( GF \times d\)=38
Try this beautiful problem from Geometry based on the Area of a Circle.
Area of Circle | AMC-8, 2008 | Problem 25
Margie's winning art design is shown. The smallest circle has radius 2 inches, with each successive circle's radius increasing by 2 inches. Approximately what percent of the design is black?
$44$
$42$
$45$
Key Concepts
Geometry
Area
Circle
Check the Answer
Answer:$42$
AMC-8, 2008 problem 25
Pre College Mathematics
Try with Hints
Area of the square is \(\pi (r)^2\),where \(r\)=radius of the circle
Can you now finish the problem ..........
Find the total area of the black region........
can you finish the problem........
Given that The smallest circle has radius 2 inches, with each successive circle's radius increasing by 2 inches .
The radius of the 1st circle is 2, So the area is \(\pi(2)^2\)=4\(\pi\) sq.unit
The radius of the 2nd circle is 4, So the area is \(\pi(4)^2\)=16\(\pi\) sq.unit
The radius of the 3rd circle is 6 So the area is \(\pi(6)^2\)=36\(\pi\) sq.unit
The radius of the 4th circle is 8, So the area is \(\pi(8)^2\)=64\(\pi\) sq.unit
The radius of the 5th circle is 10, So the area is \(\pi(10)^2\)=100\(\pi\) sq.unit
The radius of the 6th circle is 12, So the area is \(\pi(12)^2\)=144\(\pi\) sq.unit
Therefore The entire circle's area is 144\(\pi\)
The area of the black regions is \((100\pi-64\pi)+(36\pi-16\pi)+4\pi=60\pi \)sq.unit
The percentage of the design that is black is \((\frac{60\pi}{144\pi} \times 100)\%=(\frac{5}{12} \times 100) \% \approx 42\%\)
