Who wants a scoop?

Geometry Level 1

A spherical scoop of ice cream has the same radius as the base of a cone. The heights of the cone and the scoop of ice cream are the same.

If the sphere of ice cream were to melt, then how many ice cream cones of this type could it fill?


The answer is 2.

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8 solutions

let V s \large V_s be the volume of the sphere and V c \large V_c be the volume of the cone

since their heights are equal, the height of the cone must be 2 r \large 2r

V s = 4 3 π r 3 \large V_s=\dfrac{4}{3}\pi r^3

V c = 1 3 π r 2 ( h ) = 1 3 π r 2 ( 2 r ) = 2 3 π r 3 \large V_c=\dfrac{1}{3}\pi r^2(h)=\dfrac{1}{3}\pi r^2(2r)=\dfrac{2}{3}\pi r^3

let n n be the number of ice cream cones, so

n = V s V c = 4 3 2 3 = 4 3 × 3 2 = 4 2 = \large n= \dfrac{V_s}{V_c}=\dfrac{\frac{4}{3}}{\frac{2}{3}}=\dfrac{4}{3} \times \dfrac{3}{2}=\dfrac{4}{2}= 2 \color{#D61F06}\large \boxed{2}

Andrew Ellinor
Oct 19, 2015

Because the ice cream is a sphere with radius r r , it has volume 4 3 π r 3 \dfrac{4}{3}\pi r^3 .

On the other hand, the volume of the cone is 1 3 π r 2 h = 1 3 π r 2 ( 2 r ) = 2 3 π r 3 \dfrac{1}{3}\pi r^2h = \dfrac{1}{3}\pi r^2 (2r) = \dfrac{2}{3}\pi r^3 , exactly half that of the volume of the ice cream. Therefore, two ice cream cones can be filled with melted ice cream.

Correct. Unfortunately, 30 to 50 per cent of the emulsion - the perfect 'sphere' of ice cream - is composed of air, thus considerably reducing the volume of melted ice cream to much less than the volume of two cones.

Fabio Bittar - 5 years, 7 months ago

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Fun fact Fabio!

Grant Petersen - 2 years, 1 month ago

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so, to Summarise, Ice cream has won against lay's

I Love Brilliant - 10 months, 4 weeks ago
Achille 'Gilles'
Oct 19, 2015

Let x x be the number of required ice cream cones. Then we have

x = volume of sphere volume of cone = 4 3 π ( r 3 ) 1 3 π ( r 2 ) ( 2 r ) = 4 3 2 3 = 2 x=\dfrac{\text{volume of sphere}}{\text{volume of cone}}=\dfrac{\frac{4}{3}\pi (r^3)}{\frac{1}{3}\pi (r^2)(2r)}=\dfrac{\frac{4}{3}}{\frac{2}{3}}=\boxed{2}

To je to što je sad bio je u školi

Ana Pesic - 6 months, 2 weeks ago

V s p h e r e = 4 3 π r 3 V_{sphere}=\frac{4}{3}πr^3

V c o n e = 1 3 π r 2 ( 2 r ) = 2 3 π r 3 V_{cone}=\frac{1}{3}πr^2(2r)=\frac{2}{3}πr^3

V s p h e r e V c o n e = ( 4 / 3 ) ( 2 / 3 ) = 2 \frac{V_{sphere}}{V_{cone}}=(4/3)(2/3)=2

Yehuda Davis
May 6, 2016

r=radius which equals or half height .

pi r^3 4/3 is the volume of the sphere and the volume of the cone is pi r^2 h/3 .

we can divide each equation by pi and have the same ratio so we divide them and get r^3 4/3 for the sphere and r^2 h/3 for the cone .

we can then divide each equation by r^2 and have the same ratio so we divide them and get r 4/3 for the sphere and h 1/3 or 2 r 13 but we can change that to r*2/3 for the cone .

so we have 4 thirds of the radius for the sphere and 2 thirds for the cone so the volume of the sphere is double the volume of the cone

Supriyatna Pri
Oct 20, 2015

Volume of the scoop is 4/3 * phi * r^3

Volume of cone is 1/3 * phi * r^2 * t, t = 2 * r

So 4/3 * phi * r^3 = n * 1/3 * phi * r^2 * (2 * r)

                            = n * 2/3 * phi * r^3       ===>>> n = 2
Sadasiva Panicker
Oct 20, 2015

vol of cone = 1/3πr²h;h=d=2r; Therefore V=1/3πr²x2r = 2/3πr³=: Vol of sphere =4/3πr³= 2x2/3πr³ So 2 cones.

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