UPSC CDS 2 2022 Math Paper

Volume of cuboid =lbh
Total surface area of cuboid =2(lb+bh+hl)
Where, l= length, b= breadth and h= height

Volume of cuboid
xyz=400cm3
The total surface area of a cuboid
A=2(xy+yz+zx)=340cm2
⇒xy+yz+zx=170
Now, the required value
⇒x−1+y−1+z−1=‌

1

x

+‌

1

y

+‌

1

z

Using equation (1) \& (2)
⇒‌

xy+yz+zx

xyz

=‌

170

400

⇒‌

xy+yz+zx

xyz

=‌

17

40

⇒x−1+y−1+z−1=‌

17

40