1. Which of the following equations has real roots?
A. [latex]{3x}^{2} + 4x + 5 = 0[/latex]
B. [latex]{x}^{2} + x + 4 = 0[/latex]
C. (x – 1) (2x – 5) = 0
D. [latex]{2x}^{2} - 3x + 4 = 0[/latex]
Answer - Option C
Explanation -
(x – 1) (2x – 5) = 0
x = 1, x = [latex]\frac{5}{2}[/latex]
Both roots are real.
For real roots of quadratic equation
[latex]{ax}^{2}[/latex] + bx + c = 0
we have [latex]{b}^{2}[/latex] – 4ac ≥= 0
For [latex]{3x}^{2}[/latex]+ 4x + 5 = 0
[latex]{b}^{2}[/latex] – 4ac = 16 – 4 * 3 * 5 = – 44
For [latex]{x}^{2}[/latex] + x + 4 = 0
[latex]{b}^{2}[/latex] – 4ac = 1 – 4 * 1 * 4 = – 15
For [latex]{2x}^{2}[/latex] - 3x + 4 = 0
[latex]{b}^{2}[/latex]– 4ac = 9 – 4 * 2 * 4 = – 23
2. 3 chairs and 2 tables cost 700, while 5 chairs and 3 tables cost 1100. What is the cost of 2 chairs and 2 tables ?
A. 300
B. 350
C. 450
D. 600
Answer - Option D
Explanation -
Let cost of chair = x and cost of table = y
i.e, 3x + 2y = 700 ...(i)
and 5x + 3y = 1100 ...(ii)
Solving (i) and (ii) we get
x = 100 and y = 200
Now 2x + 2y = 200 + 400 = 600
3. If x = [latex]\frac{4ab}{a + b}[/latex], then value of [latex]\frac{x + 2a}{x - 2a}[/latex] + [latex]\frac{x + 2a}{x - 2a}[/latex] is equal to
A. 0
B. 1
C. 2
D. None of these
Answer - Option A
Explanation -
[latex]\frac{x + 2a}{x - 2a} + \frac{x + 2b}{x - 2b}[/latex] = [latex] \frac{\frac{6ab + {2a}^{2}}{a + b}}{\frac{2ab -{2a}^{2}}{a + b}} + \frac{\frac{2ab + {6b}^{2}}{a + b}}{\frac{2ab - {2b}^{2}}{a + b}}[/latex]
[latex]\frac {2a(3b + a)}{2a(b - a)} + {2b(3b + a)}{2b(a - b)}[/latex]
[latex]\frac {(3b + a)}{(b - a)} + {(3b + a)}{(a - b)}[/latex] = 0
4. If a = [latex]\frac{x}{x + y}[/latex] and b = [latex]\frac{y}{x - y}[/latex], then [latex]\frac{ab}{a - b}[/latex] is equal to
A. [latex]\frac{xy}{{x}^{2} + {y}^{2}}[/latex]
B. [latex]\frac {{x}^{2} + {y}^{2}} {xy}[/latex]
C. [latex]\frac{x}{x + y}[/latex]
D. [latex]\frac{y}{x - y}[/latex]
Answer - Option A
Explanation -
[latex]\frac{ab}{a + b}[/latex] = [latex]\frac{(\frac{x}{x + y}) * (\frac{x}{x - y})}{(\frac{x}{x + y}) * (\frac{y}{x - y})}[/latex]
= [latex]\frac{xy}{{x}^{2} + {y}^{2}}[/latex]
5. If [latex]\frac{y}{x - z}[/latex] = [latex]\frac{x + y}{z}[/latex] = [latex]\frac{x}{y}[/latex] determine the ratio of x : y : z
A. 1 : 2 : 3
B. 3 : 2 : 1
C. 4 : 2 : 3
D. 2 : 4 : 7
Answer - Option C
Explanation -
Substitute in the choices.
Using x = 4, y = 2, z = 3, we find the equation is satisfied
6. Sum of two numbers is 15 and sum of their reciprocals is [latex]\frac{15}{56}[/latex] The two numbers are
A. 4, 11
B. 5, 10
C. 6, 9
D. 7, 8
Answer - Option B
Explanation -
Adding all three, we get
[latex]\frac{x + y + z}{4(x + y + z)}[/latex] = a = [latex]\frac{1}{4}[/latex]
7. If a + b + c = 0, find the value of [latex]\frac{{a}^{2}}{{a}^{2} - {bc}} + \frac{{b}^{2}}{{b}^{2} - {ca}} + \frac{{c}^{2}}{{c}^{2} - {ab}}[/latex]
A. 4
B. 3
C. 1
D. None of these
Answer - Option B
Explanation -
= [latex]\frac{{a}^{2}}{{a}^{2} - {bc}} + \frac{{b}^{2}}{{b}^{2} - {ca}} + \frac{{c}^{2}}{{c}^{2} - {ab}}[/latex]
= [latex]\frac {a}{a}(\frac{{2a}^{2} - bc}{bc}) + \frac {b}{b} (\frac {{2b}^{2}-ac} - {ca}) + \frac{c}{c}(\frac{{2c}^{2} - ab} {ab})[/latex]
[Applying componendo and dividendo on each terms]
= [latex]( \frac {{2a}^{3} - abc}{abc}) + ( \frac{{2b}^{3} - abc}{abc}) + ( \frac{{2c}^{3} - abc} {abc})[/latex]
= [latex]2 ( \frac{{a}^{3} + {b}^{3} + {c}^{3}} {abc})[/latex]
[latex]\frac{6abc - 3abc}{abc}[/latex] = 3
8. If p, q, r, s are in harmonic progression and p > s, then
A. [latex] \frac{1}{ps} < \frac{1}{qr}[/latex]
B. -q + r = p + s
C. [latex] \frac{1}{p} + \frac{1}{q} = \frac{1}{r} + \frac{1}{s}[/latex]
D.None of these
Answer - Option D
Explanation -
p, q, r, s are in H. P.
= [latex] \frac{1}{p}, \frac{1}{q}, \frac{1}{r}, \frac{1}{s}[/latex] are in A.P
= [latex] \frac{1}{p} - \frac{1}{q} = \frac{1}{r} - \frac{1}{s}[/latex]
= [latex] \frac{1}{q} + \frac{1}{r} = \frac{1}{p} + \frac{1}{s}[/latex]
9. If [latex]{2x}^{2} - 7 xy + {3y}^{2}= 0[/latex], then the value of x : y is
A. 3 : 2
B. 2 : 3
C. 3 : 1 and 1 : 2
D. 5 : 6
Answer - Option C
Explanation -
[latex]{2x}^{2} - 7 xy + {3y}^{2}= 0[/latex]
= [latex]\frac{7 ± \sqrt{49 - 24} }{2 * 2}[/latex] = [latex]\frac{7 ± 5}{4} = 3 \frac{1}{2}[/latex]
Thus x : y = 3 : 1 and 1 : 2
10. The difference between the logarithms of sum of the squares of two positive numbers A and B and the sum of logarithms of the individual numbers is a constant C. If A = B, then C is
A. 2
B. 1.3031
C. log 2
D. exp (2)
Answer - Option B
11. The arithmetic mean of the series 1, 2, 4, 8, 16, ... [latex]{2}^{n}[/latex] is
A. [latex]\frac{{2}^{n} - 1}{n}[/latex]
B. [latex]\frac{{2}^{n + 1} - 1}{n + 1}[/latex]
C. [latex]\frac{{2}^{n} + 1}{n + 1}[/latex]
D. [latex]\frac{{2}^{n} - 1}{n + 1}[/latex]
Answer - Option B
Explanation -
A.M. of the series 1, 2, 4, 8, 16, ....[latex]{2}^{n}[/latex]
= [latex]\frac{Sum of (n + 1) terms of the given series}{n + 1}[/latex]
= [latex]\frac{\frac{{2}^{n + 1} - 1}{ 2 - 1}}{\frac{{2}^{n + 1} - 1}{n + 1}}[/latex]
= [latex]\frac{{2}^{n + 1} - 1}{n + 1}[/latex]
Since series is in G.P. with first term a = 1
and common ratio r = 2
Number of terms = n + 1
Sum of this series, [latex]{S}_{n + 1}[/latex] = [latex] a \frac{{r}^{n} - 1}{r - 1}[/latex]
r = 2 > 1
12. If the sum of the 6th and the 15th elements of an arithmetic progression is equal to the sum of the [latex]{7}^{th}, {10}^{th}, {12}^{th}[/latex] elements of the same progression, then which elements of the series
should necessarily be equal to zero ?
A. [latex]{10}^{th}[/latex]
B. [latex]{8}^{th}[/latex]
C. [latex]{1}^{th}[/latex]
D. None of these
Answer - Option B
Explanation -
Let a be the first term and d be common ratio of an A.P.
i.e, (a + 5d) + (a + 14d)
= (a + 6d) + (a + 9d) + (a + 11d)
a + 7d = 0
Hence 8th term = 0
13. Let [latex]{S}_{n}[/latex] denote the sum of the first ‘n’ terms of an A.P. [latex]{S}_{2n} = {3S}_{n}[/latex]. Then the ratio [latex]{S}_{3n}{S}_{n}[/latex] is equal to
Answer - Option B
Explanation -
Let a be the first term and d be the common difference of an A. P.
[latex]{S}_{n}[/latex] = [latex]\frac{n}{2}(2a + (n - 1)d)[/latex]
[latex]{S}_{2n}[/latex] = [latex]\frac{2n}{2}(2a + (2n - 1)d)[/latex]
[latex]{S}_{3n}[/latex] = [latex]\frac{3n}{2}(2a + (3n - 1)d)[/latex]
[latex]{S}_{2n}[/latex] = [latex]{3S}_{n}[/latex]
n{2a + (2n – 1) d} = 3 * [latex]\frac{n}{2}(2a + (2n - 1)d)[/latex]
4a + (4n – 2) d = 6a + (3n – 3) d
(n + 1) d = 2a
d = [latex]\frac{2a}{n + 1}[/latex]
i.e, [latex]{S}_{n}[/latex] = [latex]\frac{n}{2}(2a + (n - 1) \frac{2a}{n + 1})[/latex] = [latex]\frac{{2an}^{2}}{n + 1}[/latex]
and [latex]{S}_{3n}[/latex] = [latex]\frac{3n}{2}(2a + (3n - 1)\frac{2a}{n + 1})[/latex] = [latex]\frac{{12an}^{2}}{n + 1}[/latex]
[latex]\frac{{S}_{n}}{{S}_{3n}}[/latex] = 6
14. The term independent of x in the expansion of [latex] {2x + \frac{1}{3x}}^{6}[/latex] is
A. [latex]\frac{160}{9}[/latex]
B. [latex]\frac{80}{9}[/latex]
C. [latex]\frac{160}{27}[/latex]
D. [latex]\frac{80}{3}[/latex]
Answer - Option C
15. Find the term independent of x in [latex] {({3x}^{2} - \frac{2}{{x}^{2}})}^{20}[/latex]
A. 126070 * [latex]{3}^{18} * {2}^{9}[/latex]
B. 184756 * [latex]{3}^{10} * {2}^{10}[/latex]
C. 120000 * [latex]{3}^{20} * {2}^{19}[/latex]
D. 320 * [latex]{{3}^{4}}^{20} * {2}^{21}[/latex]
Answer - Option B