Balancing Problem - Part 4

Algebra Level 1

In the above diagram, both beams are balanced.

How many pentagons would it take to balance 4 clouds?

3 pentagons 5 pentagons 4 pentagons 2 pentagons

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6 solutions

Patrick Engelmann
Apr 25, 2015

1 P = 1 1P = 1 Pentagon

1 C = 1 1C = 1 Cloud

1 S = 1 1S = 1 Star

We can write the following equations:

2 P = 2 C + 1 S 2P = 2C + 1S

1 C + 1 P + 1 S = 1 C + 3 S 1C + 1P + 1S = 1C + 3S

Now, we can rewrite those equations to:

2 P = 2 C + 1 S 4 P = 4 C + 2 S 2P = 2C + 1S \Leftrightarrow \boxed{4P = 4C + 2S}

1 C + 1 P + 1 S = 1 C + 3 S 1 P + 1 S = 3 S 1 P = 2 S 1C + 1P + 1S = 1C + 3S \Leftrightarrow 1P + 1S = 3S \Leftrightarrow \boxed{1P = 2S}

Now, let's put the 2 S = 1 P 2S = 1P from the second equation into the first equation:

4 P = 4 C + 2 S 4 P = 4 C + 1 P 3 P = 4 C 4 P = 4C + 2S \Leftrightarrow 4P = 4C + 1P \Leftrightarrow 3P = 4C

Thus, we need 3 3 Pentagons to balance 4 4 Clouds.

Gut erklärt!

Otto Bretscher - 6 years, 1 month ago
Rishabh Tripathi
Apr 24, 2015

Let pentagon = p = p , cloud = c =c and star = s =s

Then, 2 p = 2 c + s 2p = 2c+s ........ (1)

& c + p + s = 3 s + c c+p+s=3s+c

= > p + s = 3 s => p+s=3s

= > s = p 2 => s=\frac{p}{2}

put this value in equation (1)

2 p = 2 c + p 2 2p=2c+\frac{p}{2}

2 c = 3 p 2 2c=\frac{3p}{2}

Multiply by 2

4 c = 3 p \boxed{4c=3p}

Parth Panchal
Apr 26, 2015

x=pentagon , y=cloud ,z=star

Now from figure

2x=2y+z --------> (1)

and

x+y+z=y+3z

therefore, x=2z

.Multiplying equation (1) by 2 and substituting x=2z

we get 4y+x=4x

Thus 4y=3x

Thus Four Clouds Equal to 3 Pentagon :D

Great solving by substitution!

Chung Kevin - 6 years, 1 month ago

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Thank you Sir!

Parth Panchal - 6 years, 1 month ago

let P=1 penta, C=1cloud, S=1star

translate the first and second balance into an eqation; 2P=2C+S (1st balance) S+P+C=C+3S (2nd balance)

combine similar terms in 2nd equation, S+P+C=C+3S P=2S S=P/2 (substitute to the 1st equation)

2P=2C+(P/2) 3P/2=2C 3P=4C

3 Pentagon is needed to balance 4 clouds

Good solution!

Chung Kevin - 6 years, 1 month ago
Adnan Mughanni
Apr 27, 2015

We can simply solve it from the condition of the first digram .

weight of 2penta = weight of ( 2cloud + 1 star) this is first condition.

for the the required 4 clouds ,

using condition 1. let 1star = 1cloud .

that is 2penta= 2cloud + 1cloud 2penta= 3clouds

as there are 4 clouds so : adding 1 weight on both sides 1penta + 2penta = 3cloud + 1cloud that is

            3penta = 4clouds

hence penta for 4 clouds = 3 Ans.

It is not true that "1 star = 1 cloud".

Chung Kevin - 6 years, 1 month ago

Since you need 1 star along with 2 clouds to balance the beam with 2 pentagons on the other side, clouds are LIGHTER! So, for 4 clouds you'll need 3 pentagons.

How did you know that it's not 2 pentagons?

Chung Kevin - 6 years, 1 month ago

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