Q 1 :

If |x+3|+xx+2>1, then x∈

  • (-5,-2)

     

  • (-1,∞)

     

  • (-5,-2)∪(-1,∞)

     

  • none of these

     

(3)

We have,  |x+3|+xx+2>1

⇒ |x+3|+xx+2-1>0⇒|x+3|-2x+2>0

Now, two cases arise:

Case I: Whenx+3≥0, i.e., x≥-3.

Then,  |x+3|-2x+2>0⇒x+3-2x+2>0⇒x+1x+2>0

⇒ {x+1>0 and x+2>0} or {x+1<0 and x+2<0}

⇒ {x>-1 and x>-2} or {x<-1 and x<-2}

⇒ x>-1 or x<-2

⇒ x∈(-1,∞) or x∈(-∞,-2)

⇒ x∈[-3,-2)∪(-1,∞)    [Since x≥-3]         ...(i)

Case II: When x+3<0, i.e., x<-3.

Then,  |x+3|-2x+2>0⇒-x-3-2x+2>0

⇒-(x+5)x+2>0⇒x+5x+2<0

⇒ {x+5<0 and x+2>0} or {x+5>0 and x+2<0}

⇒ {x<-5 and x>-2}  which is not possible,

       or {x>-5 and x<-2}

⇒ x∈(-5,-2)

⇒ x∈(-5,-3)    [Since x<-3]                  ...(ii)

Combining (i) and (ii), the required solution is

x∈(-5,-2)∪(-1,∞)



Q 2 :

Solution of |3x+2|<1 is

  • [-1,-13]

     

  • {-13,-1}

     

  • (-1,-13)

     

  • None of these

     

(3)

We have,  

|3x+2|<1⇔-1<3x+2<1⇔-3<3x<-1⇔-1<x<-13



Q 3 :

Solution of  2x-1=|x+7| is

  • - 2

     

  • 8

     

  • - 2, 8

     

  • None of these

     

(2)

2x-1=|x+7|={x+7,if x≥-7-(x+7)if x<-7

∴  If x≥-7,  2x-1=x+7⇒x=8

        If x<-7,  2x-1=-(x+7)⇒3x=-6

⇒ x=-2,  Not possible.



Q 4 :

Solution of  0<|3x+1|<13 is

  • (-49,-29)

     

  • [-49,-29]

     

  • (-49,-29)-{-13}

     

  • [-49,-29]-{-13}

     

(3)

Let us first solve |3x+1|<13

⇔-13<3x+1<13⇔-43<3x<-23

⇔-49<x<-29

Also, 0<|3x+1| is satisfied by each x except when

3x+1=0, i.e., x=-13

∴  Solution is (-49,-29)-{-13}



Q 5 :

The set of real values of x satisfying the inequality 

|x2+x-6|>6, is

|x-2|+|x+2|<4 is

  • (-4,3)

     

  • (-3,2)

     

  • (-4,-3)∪(2,3)

     

  • (-4,-1)∪(0,3)

     

(4)

We have,  |x2+x-6|<6

⇒ -6<x2+x-6<6

⇒ -6<x2+x-6  and  x2+x-6<6

⇒ x2+x>0  and  x2+x-12<0

⇒ x(x+1)>0  and  (x+4)(x-3)<0

⇒ x∈(-∞,-1)∪(0,∞)  and  -4<x<3

⇒ x∈(-4,-1)∪(0,3)



Q 6 :

For |x-1|x+2<1, x lies in the interval

  • (-∞,-2)∪(-12,∞)

     

  • (-∞,1)∪[2,3]

     

  • (-∞,-4)

     

  • [-12,1]

     

(1)

Case I:  |x-1|=x-1,  x≥1

∴  |x-1|x+2<1⇒x-1x+2<1⇒x-1x+2-1<0⇒-3x+2<0

⇒ 3x+2>0  which is possible when x>-2

But it is true for x≥1, so common solution is x≥1 or x∈[1,∞)           ...(i)

Case II:  |x-1|=-x+1, x<1

∴  |x-1|x+2<1⇒-x+1x+2<1⇒x-1x+2+1>0⇒2x+1x+2>0

⇒ x<-2  or  x>-12

But x<1, so x∈(-∞,-2)∪(-12,1)                  ...(ii)

∴  From (i) and (ii), x lies in the interval

(-∞,-2)∪(-12,1)∪[1,∞)    or    x∈(-∞,-2)∪(-12,∞)



Q 7 :

The set of all real x satisfying the inequality  3-|x|4-|x|≥0 is

  • [-3,3]∪(-∞,-4)∪(4,∞)

     

  • (-∞,-4)∪(4,∞)

     

  • (-∞,-3)∪(4,∞)

     

  • (-∞,-3)∪(3,∞)

     

(1)

Case I: When x≥0

∴  |x|=x

⇒ 3-|x|4-|x|=3-x4-x≥0⇒(3-x)(4-x)(4-x)2≥0

⇒ (x-3)(x-4)≥0 and x≠4⇒x≤3 or x>4

But x≥0, so x∈[0,3]∪(4,∞)                                    ...(i)

Case II: When x<0

∴  |x|=-x

⇒ 3-|x|4-|x|=3+x4+x≥0⇒(x+3)(x+4)(x+4)2≥0

⇒ (x+3)(x+4)≥0 and x≠-4

⇒ x<-4 or x≥-3

But x<0, so x∈(-∞,-4)∪[-3,0)                         ...(ii)

From (i) and (ii), x lies in the interval

(-∞,-4)∪[-3,3]∪(4,∞)



Q 8 :

Solution of |x-1|≥|x-3| is

  • x≤2

     

  • x≥2

     

  • [1, 3]

     

  • None of these

     

(2)

We have,  |x-1|-|x-3|≥0

Also, |x-1|-|x-3|={-2,if x<12x-4,if 1≤x≤32,if x>3

If x<1⇒-2≥0, not possible

If 1≤x≤3

⇒2x-4≥0⇒x≥2⇒x∈[2,∞)⇒x∈[2,3]

If x>3

⇒2≥0⇒x∈(3,∞)

Combining above, we get  x∈[2,∞)



Q 9 :

If |2x-3|<|x+5|, then x lies in the interval

  • (-3, 5)

     

  • (5, 9)

     

  • (-23,8)

     

  • (-8,23)

     

(3)

We have,  |2x-3|<|x+5|                  ...(i)

Let x≥32, then 2x-3≥0 and x+5≥0

Thus, 2x-3<x+5⇒x<8

Thus x∈[32,8) satisfies the above inequality for x≥32

Now, let -5≤x<32

Then, 2x-3<0 and x+5≥0

So, 3-2x<x+5⇒3x>-2⇒x>-23

But, -5≤x<32

Thus, x∈(-23,32) satisfies the given inequality (i).

Also, let x<-5. Then, 2x-3<0 and x+5<0

⇒3-2x<-5-x⇒x>8                           ...(ii)

However, x<-5

∴  The above inequality (ii) does not hold.

We have checked all the required intervals.

∴  x∈[32,8)∪(-23,32)⇒x∈(-23,8)



Q 10 :

The solution of 6x4x-1<12 is

  • x<-18

     

  • -18<x<14

     

  • x<-18 and x>14

     

  • x>18

     

(2)

Given inequality is, 6x4x-1<12⇒12x4x-1<1

⇒12x4x-1-1<0⇒8x+14x-1<0                 …(i)

For above inequality (i), we have two cases either

(I)  8x+1>0, 4x-1<0  or  (II)  8x+1<0, 4x-1>0

From (I), we get  x>-18, x<14

∴   x∈(-18,14)                                 …(ii)

From (II), x<-18, x>14, both of which can not be true

∴    (ii) represents the solution set of given inequality.



Q 11 :

If  |x-1|+|x-3|≤8, then the values of x lie in the interval

  • (-∞,-2]

     

  • [-2, 6]

     

  • (-3, 7)

     

  • (-2,∞)

     

(2)

Here two cases arises,

Case 1: When -∞<x≤1

Then, (x-1)≤0, x-3<0

⇒ |x-1|=-(x-1)  and  |x-3|=-(x-3)

Now,  |x-1|+|x-3|≤8 ⇒ -(x-1)-(x-3)≤8

⇒ -2x+4≤8⇒x≥-2           …(i)

Case 2: When 3≤x<∞

∴  |x-1|=(x-1)  and  |x-3|=(x-3)

Now, |x-1|+|x-3|≤8

⇒ x-1+x-3≤8⇒2x-4≤8⇒x≤6          …(ii)

From (i) and (ii), we get x∈[-2, 6]



Q 12 :

If  |x-2|≤1, then

  • x∈(1, 3)

     

  • x∈(-1, 3)

     

  • x∈[1, 3]

     

  • x∈[-1, 3)

     

(3)

Here, |x-2|≤1

⇒ -1≤x-2≤1⇒1≤x≤3⇒x∈[1, 3]



Q 13 :

If  |x-3|x-3>0, then

  • x∈(-3,∞)

     

  • x∈(3,∞)

     

  • x∈(2,∞)

     

  • x∈(1,∞)

     

(2)

Given, |x-3|x-3>0

⇒ |x-3|>0⇒x-3>0⇒x>3

∴  x∈(3,∞)



Q 14 :

If  |x+5|≥10, then

  • x∈(-15, 5]

     

  • x∈(-5, 5]

     

  • x∈(-∞,-15]∪[5,∞)

     

  • x∈[-∞,-15]∪[5,∞)

     

(3)

We know that |x-a|≥r

⇔ x≤a-r or x≥a+r

∴  |x+5|≥10⇔x≤-5-10, or x≥-5+10

⇔ x≤-15 or x≥5⇔x∈(-∞,-15] or x∈[5,∞)

⇔ x∈(-∞,-15]∪[5,∞)



Q 15 :

The solution set of the rational inequality x+9x-6≤0 is

  • (-∞,9)∪(6,∞)

     

  • (-∞,9]∪(6,∞)

     

  • (-∞,9]∪[6,∞)

     

  • [-9, 6)

     

(4)

We have, x+9x-6≤0

Case I: x+9≥0 and x-6<0

⇒ x≥-9 and x<6⇒-9≤x<6            …(i)

Case II: x+9≤0 and x-6>0⇒x≤-9 and x>6

which is not possible simultaneously.

∴  Required solution set is  [-9, 6).



Q 16 :

The solution set of the inequality -2≤3x+22<7 is

  • {x:3≤x<4}

     

  • {x:-2≤x<3}

     

  • {x:-2≤x<4}

     

  • {x:0≤x<6}

     

(3)

We have, -2≤3x+22<7

⇒ -4≤3x+2<14⇒-6≤3x<12⇒-2≤x<4



Q 17 :

Which of the following is incorrect for the solution set of the inequation ||x|-1|<|1-x|, x∈R, is

  • (-1, 1)

     

  • (0, ∞)

     

  • (-1, ∞)

     

  • (-∞, -1)

     

Select one or more options

(1, 2, 3)

Let us consider the following cases:

Case I: When x≥0

In this case, we have |x|=x

∴   ||x|-1|<|1-x|

⇒ |x-1|<|x-1|, which is not true for x≥0

Case II: when x<0

|x|=-x

∴  ||x|-1|<|1-x|

        =|-x-1|<|1-x|=|x+1|<|x-1|

If x<-1, then |x+1|=-(x+1) and |x-1|=-(x-1)

∴  |x+1|<|x-1|=-(x+1)<-(x-1)

⇒ -1<1, which is always true.

Thus, (-∞,-1) is the solution set.

If -1<x<0, then |x+1|=x+1, |x-1|=-(x-1)

∴  |x+1|<|x-1|=x+1<-(x-1)⇒2x<0⇒x<0

But, -1<x<0.

Therefore, x∈(-1,0).

Hence, (-∞,0) is the solution set.



Q 18 :

If mx2-9mx+5m+1>0 and m∈[p,q16), then p+q= _________ .



(4)

mx2-9mx+(5m+1)>0

⇒ m>0 and D<0⇒m(61m-4)<0

⇒ m∈[0,461)⇒p=0, q=4

∴ p+q=4



Q 19 :

If n=1983!, then the value of expression 1log2n+1log3n+1log4n+⋯+1log1983n is _________.



(1)

1log2n+1log3n+1log4n+⋯+1log1983n

=logn2+logn3+⋯+logn1983

=logn(2·3·4⋯1983)=logn1983!=lognn=1



Q 20 :

The value of (127)2-(log5162log59)=0.pq, then p+q= ________ .



(1)

2-log5162log59=2-log516log581=2-log8116

=2-log32=log39-log32=log392

(127)log392=(3-32)log392=3log3(92)-32

(92)-32=(29)32=2227=0.10=0.pq

∴  p+q=1+0=1



Q 21 :

If (3x)log3=(4y)log4, 4logx=3logy then x+yx-y= __________.



(7)

Taking log on both sides, we get

log3 (log3+logx)=log4 (log4+logy)

logx·log4=logy·log3

⇒  logx=-log3, logy=-log4

⇒  x=13, y=14⇒x+yx-y=7



Q 22 :

Number of integers in the solution set of |x-1|log2(4-x)<|x-1|log2(1+x) are ________.



(2)

4-x>0, 1+x>0⇒x∈(-1,4)            ⋯(i)

Let |x-1|<1⇒x∈(0,2)                         ⋯(ii)

The inequality implies log2(4-x)>log2(1+x)

⇒  4-x>1+x

⇒  x<32                                                ⋯(iii)

From (i), (ii) and (iii) ⇒  x∈(0,32)

Let |x-1|>1⇒x∈(-∞,0)∪(2,∞)       ⋯(iv)

The inequality implies  log2(4-x)<log2(1+x)

⇒  4-x<1+x⇒x>32                            ⋯(v)

(i), (iv), (v) ⇒x∈(2,4)

Finally, we have  x∈(0,32)∪(2,4)

∴    Number of integers = 2



Q 23 :

A manufacturer has 800 L of a 10% solution of acid. The range of 35% acid to be added to it is (a, b) such that the acid content in the resultant mixture will be more than 15% but less than 25%, then a+b= ________.



(1400)

Let x L of 35% acid solution is added to the solution.

Total mixture=(x+800) L

According to question,

             35% of x+10% of 800>15% of (x+800)

and       35% of x+10% of 800<25% of (x+800)

∴  15100(800+x)<35100x+10100×800

and     25100(800+x)>35100x+10100×800

⇒  12000+15x<35x+8000  and  20000+25x>35x+8000

⇒  4000<20x  and  12000>10x

⇒  200<x  and  1200>x  i.e.,  200<x<1200

Thus,  a=200,  b=1200

Hence, a+b=200+1200=1400