Question

From a cuboid solid metallic mark of dimensions $15cm\times 10cm\times 5cm$ a cylindrical hole of diameter 7 cm is drilled out. Find the surface area of the remaining block $[Use\pi =\frac{22}{7}]$

Answer 1

Since, we drilled out a cylinder in a inbold, we got a neq cylindrical surface shown by datd protion in th efigure.
Also we need to subtract the upper and lower circular surfaces as they we no more the part of the cuboid
Surface area of remaining block : - Surface area + surface area - Area of top and bottom of cuboid of cylinder circular surfaces
$=2(150+50+75)+2\pi rh-2\pi r^2$
$=550+\text{/}2\times \frac{22}{7}\times \frac{7}{2}\times 5-\text{/}2\times \frac{\text{/}22}{7}\times \frac{7}{2}\times \frac{7}{2}=550+110-77$
$660-77=583cm$