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Re: The flying acrobatic team is made up of 120 airplanes. The team wants [#permalink]
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Bunuel wrote:
The flying acrobatic team is made up of 120 airplanes. The team wants to form a rectangular formation with X planes in a row and Y planes in a column. If the number of airplanes in a row is no less than 4 and no more than 30, how many different combinations of rectangular shapes are possible?

A. 4.
B. 5.
C. 6.
D. 8.
E. 10.


If x are the rows and Y are the colums then

Total Number of Airplanes = X*Y = 120

i.e. X*Y = 1*120
2*60
3*40
4*30
5*24
6*20
8*15
10*12


There are 5 combinations of X*Y but X and Y can be interchanged hence there are 10 possibilities for X as well as for Y

Answer: option E
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Re: The flying acrobatic team is made up of 120 airplanes. The team wants [#permalink]
There's a way that may not necessarily be used this time, but comes in handy in more complicated examples:

First let's do the prime factorization:
120|2
60 |2
30 |2
15 |3
5 |5
1

hence 120= (2^3)*(3^1)*(5^1)

This implies that 120 has in total: (3+1)(1+1)(1+1)=4*2*2=16 factors, which makes 8 pairs of factors that can form a rectangle of an area equal to 120. Since factors 1, 2 and 3 cannot be used, we are left to 8-3=5 pairs of facors. 5 pairs = 10 facors

Asnwer: E
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Re: The flying acrobatic team is made up of 120 airplanes. The team wants [#permalink]
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Re: The flying acrobatic team is made up of 120 airplanes. The team wants [#permalink]
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