1600 satellites were sent up by a country for several purposes. The purposes are classified as broadcasting (B), communication (C), surveillance (S), and others (O). A satellite can serve multiple purposes; however a satellite serving either B, or C, or S does not serve O.
The following facts are known about the satellites:
1. The numbers of satellites serving B, C, and S (though may be not exclusively) are in the ratio 2:1:1.
2. The number of satellites serving all three of B, C, and S is 100.
3. The number of satellites exclusively serving C is the same as the number of satellites exclusively serving S. This number is 30% of the number of satellites exclusively serving B.
4. The number of satellites serving O is the same as the number of satellites serving both C and S but not B.
Question No. 1:
What best can be said about the number of satellites serving C?
Options:
- Must be between 450 and 725
- Cannot be more than 800
- Must be between 400 and 800
- Must be at least 100
Question No. 2:
What is the minimum possible number of satellites serving B exclusively?
Options:
- 100
- 200
- 500
- 250
Question No. 3:
If at least 100 of the 1600 satellites were serving O, what can be said about the number of satellites serving S?
Options:
- At most 475
- Exactly 475
- At least 475
- No conclusion is possible based on the given information
Question No. 4:
If the number of satellites serving at least two among B, C, and S is 1200, which of the following MUST be FALSE?
Options:
- The number of satellites serving C cannot be uniquely determined
- The number of satellites serving B is more than 1000
- All 1600 satellites serve B or C or S
- The number of satellites serving B exclusively is exactly 250
It is given that the satellites serving either B, C or S do not serve O.
From (1), let the number of satellites serving B, C and S be 2K, K, K respectively.
Let the number of satellites exclusively serving B be x.
From (3), the number of satellites exclusively serving C and exclusively serving S will each be 0.3x
From (4), the number of satellites serving O is same as the number of satellites serving only C and S. Let that number be y.
Since the number of satellites serving C is same as the number of satellites serving S, we can say that
(number of satellites serving only B and C) + 0.3x + 100 + y = (number of satellites serving only B and S) +
0.3x + 100 + y
Let the number of satellites serving only B and C = the number of satellites serving only B and S = Z
Therefore, the venn diagram will be as follows
Given that there are a total of 1600 satellites
=> x + z + 0.3x + z + 100 + y + 0.3x + y = 1600
1.6x + 2y + 2z = 1500 --------------- (1)
Also K = 0.3x + z + y +100
Satellites serving B = 2K = x + 2z + 100
=> 2(0.3x + z + y + 100) = x + 2z + 100
0.4x = 2y + 100
x = 5y + 250 -----------(2)
Substituting (2) in (1), we will get
1.6 (5y + 250) + 2y + 2z = 1500
10y + 2z = 1100
Z = 550 – 5y ------------ (3)
Question 1:
The number of satellites serving C = z + 0.3x + 100 + y
= (550 – 5y) + 0.3(5y + 250) + 100 + y = 725 – 2.5y
This number will be maximum when y is minimum.
Minimum value of y is 0.
Therefore, the maximum number of satellites serving C will be 725.
From ③, z = 550 – 5y
Since the number of satellites cannot be negative,
$z \geq 0 \Rightarrow 550 - 5 y \geq 0$
$y \leq 110$
Maximum value of y is 110.
When y = 110, the number of satellites serving C will be 725 – 2.5 × 110 = 450. This will be the minimum
number of satellites serving C.
The number of satellites serving C must be between 450 and 725.
Question 2:
From 2, the number of satellites serving B exclusively is x = 5y + 250
This is minimum when y is minimum.
Minimum value of y = 0.
The minimum number of satellites serving B exclusively = 5 × 0 + 250 = 250.
Question 3:
Given that at least 100 satellites serve 0; we can say in this case that y ≥ 100.
Number of satellites serving s = 0.3x + z +100 + y=725 – 2.5y
This is minimum when y is maximum, i.e. 110, (from③)
Minimum number of satellites serving = 725 – 2.5 ×100 = 450.
This is maximum when y is minimum, i.e., 100 in this case.
Maximum number of satellites serving = 725 – 2.5 ×100 = 475
Therefore, the number of satellites serving S is at most 475
Question 4:
The number of satellites serving at least two of B, C or S = number of satellites serving exactly two of
B, C or S + Number of satellites serving all the three
= z + z + y + 100
= 2(550 – 5y) + y + 100
= 1200 – 9y.
Given that this is equal to 1200
1200 – 9y = 1200
=> y = 0
If y = 0, x = 5y + 250 = 250
z = 550 – 5y = 550
No. of satellites serving C = k = z + 0.3x + 100 + y
= 550 + 0.3 250 + 100 + y
= 725
No. of satellites serving B = 2k = 2 725 = 1450.
From the given options, we can say that the option “the number of satellites serving C cannot be uniquely determined” must be FALSE
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