Empty The Punchbowl

Geometry Level 2

Image source: [opensky.com]

A hemispherical punch bowl of internal radius 9 9 cm is full to the brim with fruit punch. This liquid is transferred into small cylindrical bottles with diameter 3 cm and height 4cm. How many bottles can be filled before the punchbowl is empty?


The answer is 54.

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6 solutions

Prasun Biswas
Dec 25, 2013

Since the liquid just goes from one container to other containers, the total volume of the liquid remains the same.

Let n n be the required no. of cylindrical bottles.

Volume of total liquid in hemispherical bowl = 2 3 π r 3 = 2 3 π ( 9 ) 3 =\frac{2}{3} \pi r^3 = \frac{2}{3} \pi (9)^3 c m 3 cm^3

Volume of liquid in one bottle = π r 2 h = π ( 3 2 ) 2 × 4 =\pi r^2 h = \pi (\frac{3}{2})^2 \times 4 c m 3 cm^3

We have, 2 3 π ( 9 ) 3 = n π ( 3 2 ) 2 × 4 \frac{2}{3} \pi (9)^3=n \pi (\frac{3}{2})^2 \times 4

2 3 × 729 = n ( 9 4 ) × 4 \implies \frac{2}{3} \times 729=n(\frac{9}{4}) \times 4

2 × 243 = 9 n n = 54 \implies 2\times 243=9n \implies n=\boxed{54}

So, no. of bottles required = n = 54 =n=\boxed{54}

nice one Prasoon.

Soham Dibyachintan - 7 years, 5 months ago

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bro, you got my name wrong...its Prasun.

Prasun Biswas - 7 years, 5 months ago

Brilliant :P

Gautam Mahapatra - 7 years, 3 months ago
Tarun Mathur
Dec 24, 2013

V. of hemisphere=2/3 22/7 9 9 9 (i) V.of cylinder=22/7 3/2 3/2*4 (ii)

                           (i)/(ii)

=1527/28=54 bottles (ANS.)

Sameer Arora
Dec 24, 2013

the volume of the liquid in the hemispherical bowl remains same when it is transfered to the cylindrical bottles. therefore,

volume of liquid in the bowl = total volume of liquid in the cylinders

2 3 π 9 9 9 \frac {2}{3} * {\pi} * 9*9*9 = n π 3 2 3 2 4 {\pi}*\frac {3}{2}* \frac {3}{2}*4 , where n is the number of cylinders .

hence, n = 54 \boxed {54}

Budi Utomo
Dec 24, 2013

1/2.V ball = k.V bottle ---> 2/3 . phi . r ball^3 = k . phi . r bottle^2 . t_bottle ---> 2/3 . 9^3 = k . (3/2)^2 . 4 ---> 2 . 3 . 9^2 = k . 3^2 ---> k = 54. So, bottles will be needed to empty the bowl are 54. Answer : 54

Raj Magesh
Dec 24, 2013

To find the number of bottles needed to empty the bowl, we need to find the ratio of the volume of the bowl to the volume of each bottle. The volume of a sphere of radius r r is given by 4 3 π r 3 \dfrac{4}{3}\pi r^{3} and the volume of a right cylinder is given by π r 2 h \pi r^{2}h , where r r is the radius of the base and h h is the height of the cylinder.

2 3 π r 3 π ( 3 2 ) 2 4 = 54 \dfrac{\dfrac{2}{3}\pi r^{3}}{\pi\left(\dfrac{3}{2}\right)^{2}4} = \boxed{54}

And pardon me, r = 9 r = 9 and I did not mention that in the numerator of the ratio. Oops. :D

Raj Magesh - 7 years, 5 months ago
Rohit Nair
Dec 24, 2013

Volume of bowl = (2/3pi x 9 x 9 x 9) = 486pi

Volume of one bottle = (pi x 3/2 x 3/2 x 4) = 9pi

No. of bottles = (486pi/9pi) = 54

ncert question

pulkit kogta - 7 years, 5 months ago

This question is present in BMA IIT Foundation and Olympiad Explorer for class 9.

Rohit Nair - 7 years, 5 months ago

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