CRE 1 - Basics | Algebra - Inequalities & Modulus
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Which of the following sets represents the set of all real numbers lying between 3 and 11 excluding 3 and 11?
- (a)
[3, 11]
- (b)
(3, 11)
- (c)
[3, 11)
- (d)
(3, 11]
- (e)
(-∞, 3) ∪ (11, ∞)
Answer: Option B
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Explanation :
Range from a, b excluding both can be represented as (a, b)
∴ The required answer is (3, 11)
Hence, option (2).
Workspace:
Which of the following sets represents the set of all real numbers lying between 3 and 11 excluding 3 but including 11?
- (a)
[3, 11]
- (b)
(3, 11)
- (c)
[3, 11)
- (d)
(3, 11]
- (e)
(-∞, 3) ∪ (11, ∞)
Answer: Option D
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Explanation :
To include the end point we use square bracket [ or ] whereas to exclude it we use open bracket ( or ).
∴ The required answer is (3, 11]
Hence, option (3).
Workspace:
If a and b are two negative numbers, the which of the following is not always negative
- (a)
a + b
- (b)
a - b
- (c)
b - a
- (d)
a2b3
- (e)
Both (b) and (c)
Answer: Option E
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Explanation :
If a and b are always negative, then
Option (a): a + b will always be negative
Option (b): a - b may be positive or negative depending on the values of a and b.
Option (c): b - a may be positive or negative depending on the values of a and b.
Option (d): a2b3 will always be negative.
Hence, option (e).
Workspace:
If a, b and c are three distinct positive numbers, then (a - b)(b - c)(c - a) is always
Type 1 for Positve
Type 2 for Negative
Type 3 for Cannot be determined
Answer: 3
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Explanation :
Case 1: Let us take a = 3, b = 2 and c = 1
Now, (a - b)(b - c)(c - a) = (3 - 2)(2 - 1)(1 - 3) = -2
∴ (a - b)(b - c)(c - a) is negative.
Case 2: Let us take a = 3, b = 1 and c = 2
Now, (a - b)(b - c)(c - a) = (3 - 1)(1 - 2)(2 - 3) = 2
∴ (a - b)(b - c)(c - a) is positive.
∴ (a - b)(b - c)(c - a) can be either positive or negative.
Hence, 3.
Workspace:
If p, q, r and s are real numbers then which of the following is always true?
- (a)
If p > q and r > s, then pr > qs
- (b)
If p > q and r > s, then p - r > q - s
- (c)
If p > q and q > r, then p > q > r
- (d)
All of these
Answer: Option C
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Explanation :
Option (a): Let p = 10, q = -5, r = -2 and s = -3
Now, pr = -20 while qs = 6
∴ pr < qs
⇒ option (a) is not necessarily true
Option (b): Let p = 10, q = -5, r = -2 and s = -30
Now, p - r = 12 while q - s = 25
∴ p - r < q - s
⇒ option (b) is not necessarily true
Option (c): This is a standard result.
Hence, option (c).
Workspace:
What is the value of |(4 - 3)(3 - 6)(2 - 1)|?
Answer: 3
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Explanation :
Given, |(4 - 3)(3 - 6)(2 - 1)|
= |1 × -3 × 1|
= |-3|
= 3
Hence, 3.
Workspace:
If x, y and z are all negative numbers, then x3y2z is
Type 1 for Positive
Type 2 for Negative
Type 3 for Cannot be determined
Answer: 1
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Explanation :
Since x is negative, x3 will also be negative
y2 is always positive
z is negative
∴ x3y2z = (negative no.) × (positive no.) × (negative no.) = positive no.
Hence, 1.
Workspace:
If x is a positive number, then the least possible value of x + is?
- (a)
1
- (b)
2
- (c)
3
- (d)
4
- (e)
Cannot be determined
Answer: Option B
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Explanation :
Let us consider two numbers x and .
Now, we know for two positive numbers, AM ≥ GM
⇒ ≥
⇒ x + ≥ 2
⇒ x + ≥ 2
∴ The least possible value of x + is 2.
Hence, option (b).
Workspace:
Find the range of x if 2x + 4 > 10
- (a)
(-3, 3)
- (b)
(0, 3)
- (c)
(3, ∞)
- (d)
(-∞, 3)
Answer: Option C
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Explanation :
Given, 2x + 4 > 10
⇒ 2x > 6
⇒ x > 3
∴ x ∈ (3, ∞)
Hence, option (c).
Workspace:
When an inequality is multiplied with a negative number:
- (a)
the direction of the inequality is not affected i.e., remains the same
- (b)
the direction of the inequality changes
- (c)
the direction of the inequality may or may not change depending on the value of the number
- (d)
Cannot be determined.
Answer: Option B
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Explanation :
When an inequality is multiplied with a negative number the direction of the inequality will always change i.e., it reverses its direction.
> will become <
< will become >
≥ will become ≤
≤ will become ≥
Hence, option (b).
Workspace:
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