A spherical tank is filled with water. The radius of the sphere is 6 meters. The tank is used to fill cylindrical containers, each with a radius of 1 meter and a height of 12 meters. How many containers can be filled?
- (a)14
- (b)18
- (c)24
- (d)30
Answer
Why
Correct — C. The sphere's water is shared among the cylinders, so divide one volume by the other.
Volume of sphere = 4⁄3 π r³ = 4⁄3 π × 6³
= 4⁄3 π × 216 = 288π m³
Volume of one cylinder = π r² h = π × 1² × 12 = 12π m³
Number of containers = 288π ÷ 12π = 24 → option (c)
Why the others are wrong
- (a)14 — 14 containers hold only 14 × 12π = 168π m³, leaving 120π m³ of the sphere's 288π m³ still in the tank.
- (b)18 — 18 comes from dropping the 4⁄3 in the sphere's volume: π × 216 ÷ 12π = 18. The full volume is 288π m³, not 216π m³.
- (d)30 — 30 containers need 30 × 12π = 360π m³, more water than the 288π m³ the sphere holds.
Concept
When liquid is poured from one vessel into others, volume is conserved: the volume poured out equals the number of containers × the volume of one.
Sphere: V = 4⁄3 π r³. Cylinder: V = π r² h. Both formulas carry π, so it cancels in the division. Never multiply out 3.14 or 22⁄7 first.
The division comes out to exactly 24, so there is no leftover water. When it does not divide evenly, count only the containers that are completely filled.
Key facts
- Volume of a sphere = 4⁄3 π r³.
- Volume of a cylinder = π r² h.
- 6³ = 216, and 4⁄3 × 216 = 288.
- Containers filled = volume available ÷ volume of one container.
Study next
Common traps
- Dropping the 4⁄3 in the sphere's volume, which gives 216π ÷ 12π = 18.
- Squaring the sphere's radius instead of cubing it: 4⁄3 π × 36 = 48π, enough for only 4 containers.
Here the whole tank is poured into identical cylinders. Equating a spherical volume with a cylindrical one also decides 12 Sep 2025, 16:00, Quant Q.24, where a hemispherical stone of radius 7 cm raises the oil in a cylinder by 3 cm.
At 17 Sep 2025, 12:30, Quant Q.12 a ball of radius 4 cm displaces 256⁄3 π cm³ of water.
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