Question

A cup of $10$ cm height and $5$ cm diameter is to be made from a sheet metal of $2$ mm thickness. The number of deductions necessary will be

• A. one
• B. two
• C. three
• D. four

Answer 1

The correct option is C three

Blank size: $D=\sqrt{d^2+4dh}=\sqrt{5^2+4\times 5\times 2}$
Consider maximum possible reduction be $50$
$\Rightarrow 50=100[1-\frac{d}{15}]$
$\Rightarrow$ $d=7.5$
$\text{Next possible reduction}\to 33$
Diameter after 2nd reduction:
$=7.5\times 0.67=5.025$

$\text{3rd reduction}\to 25\%$
Thus $3$ reductions are necessary.