Shortcut Trick
Volume of cylinder = πr2h
⇒ Increase in radius = 20+20+10020×20 = 44%
⇒ Total increase/decrease = 44−3100−100×344×100
⇒ (132 - 100 - 44)/3
⇒ - 4% [(-) denote decrease ]
∴ Percentage change in volume is decreased by 4%.
Alternate MethodGiven:
Radis of cylinder is increased = 20%
Decrease of height = 3331%
Formula used:
Volume of cylinder = πr2h
(where r = radius and h = height)
Equivalent increase or decrease = ± a ± b ± (a × b)/100
Calculation:
Initial volume of cylinder = πr2h
Radius after 20% increase = r x 120/100
⇒ New radius = 6r/5
Height after 3331% = 3100%decrease = h x (100−3100%)
⇒ h x (3200%)
⇒ h x (3×100200)
⇒ New height = 32h
New volume of cylinder = π(56r)232h
⇒ New volume = 2524πr2h
Now,
Decrease in volume = πr2h - 2524πr2h
⇒ 25πr2h
Percentage decrease in volume = 25×πr2hπr2h×100
⇒ 4%
∴ Percentage change in volume is decreased by 4%.
Additional InformationPercentage increase or decrease = (New observation - old observation) x 100/ old observation
If successive increase is a% and b% then equivalent increase = a + b + (a x b)/100
If successive decrease is a% and b% then equivalent increase = - a - b + (a x b)/100
If successive increase is a% and decrease is b% then equivalent increase or decrease = a - b - (a x b)/100