Maths Olympiad Prep

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Geometry Difficulty 2.6 Junior Find the answer Canada

A closed rectangular prism with height 8 cm is standing on a face
with dimensions 2 cm by 5 cm. The prism contains water with a depth of 6
cm, as shown.

When the prism is tipped so that it stands on a face with the
greatest area, the depth of the water is

Pick one

Solution

The water is in the shape of a rectangular prism with a 2 cm by 5
cm base and depth 6 cm.

Therefore, the volume of water is $2 \text{}
cm} ×5\times 5 \text{} cm} ×6\times 6\text{} cm} = 6060\text{}
cm}^3$.

A face of the prism having the greatest area has dimensions 5 cm by 8
cm.

When the prism is tipped so that it stands on a 5 cm by 8 cm face, the
water is once again in the shape of a rectangular prism with a 5 cm by 8
cm base and unknown depth.

Suppose that after the prism is tipped, the water’s depth is dd cm.

Since the volume of water is still $60\$60\text{}
cm}^3whentheprismistipped,then when the prism is tipped, then 5 \text{} cm} ×8\times 8 \text{} cm} ×d\times d\text{}
cm} = 6060\text{} cm}^3or or 40d40d\text{}
cm}^3 = 6060\text{} cm}^3,andso, and so d=6040=32$.d=\dfrac{60}{40}=\dfrac32\$.

When the prism is tipped so that it stands on a face with the greatest
area, the depth of the water is $32\$\dfrac32 \text{} cm}=1.5$ cm.

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.