Class 9

For a particular year, following in the distribution of ages . . .

Case Study Based Question on Statistics
For a particular year, following in the distribution of ages (in years) of primary school teachers in a district :

Age (in years)	15-20	20-25	25-30	30-35	35-40	40-45	45-50
No. of Teachers	10	30	50	50	30	6	4

(a) Determine the class limits of the fourth class interval.

(b) Find the class marks of the class 45-50. Also determine the class size.

(d) How many primary school teachers are of age more than or equal to 35 years.

Doubt by Veer

Solution :

(a) Fourth Class Interval is 30-35
Lower class limit is 30
Upper Class limit is 35

(b) Class Marks & Class size of the class 45-50

Class Marks (xi)
= [LL+UL]/ 2
= [45+50]/2
= 95/2
= 47.5

Class Size (h)
= UL-LL
= 50-45
= 5

Upper limit of fifth class interval (35–40)
= 40

Sum = 15+40
= 55

(d) No. of primary school teachers which are of age more than or equal to 35 years
= 30+6+4
= 40

An angle is 24° less than its complementary angle. . .

Question : An angle is 24° less than its complementary angle. The angles measure is :

(a) 36°

(b) 33°

(d) 57°

Doubt by Veer

Solution :

Let the angle be x°
Compelent of x° = (90°-x°)

ATQ
(90°-x°)-x°=24°
90°-x°-x°=24°
90°-2x°=24°
90°-24°=2x°
66°=2x°
66°/2=x°
33°=x°
x°=33°

Hence, the correct option is (b) 33°.

If the drops of water are spherical and their diameter is 0.1 cm . . .

Question : If the drops of water are spherical and their diameter is 0.1 cm, 32000 such drops fills a conical glass up to its brim, with diameter equal to height, find the height of the glass.

Doubt by Veer

Solution :

Diameter of spherical drop (d) = 0.1 cm

Radius of spherical drop (r) = 0.1/2
=1/20 cm

For Conical Glass
D=H
2R=H
R=H/2

Volume of 32000 raindrops = volume of conical glass

32000×(4/3)πr³ = (1/3)πR²H 32000×4r³ = R²H 32000×4(1/20)³ = (H/2)²H 32000×4(1/8000) = (H²/4)H 4×4 = H³/4 4×4×4=H³ H³=(4)³ H=4 cm

Hence, the height of the glass is 4 cm

191125

Question : In the given figure, O is the centre of a circle prove that ∠x+∠ y=∠ z.

Doubt by Kashvi

Solution : Coming Soon

MCQs of Circles

MCQ Questions of Circles

1. AD is a diameter of a circle and AB is a chord. If AD=34 cm, AB=30 cm, the distance of AB from the centre of the circle is :

(A) 17 cm
(B) 15 cm
(C) 4 cm
(D) 8 cm

2. In given figure, if OA=5 cm, AB=8 cm and OD is perpendicular to AB, then CD is equal to:

(A) 2 cm
(B) 3 cm

3. If AB=12 cm, BC=16 cm and AB is perpendicular to BC, then the radius of the circle passing through the points A, B and C is:

(A) 6 cm
(B) 8 cm

4. In given figure, if ∠ABC=20º, then ∠AOC is equal to:

(A) 20º
(B) 40º
(C) 60º
(D) 10º

5. In given figure, if AOB is a diameter of the circle and AC=BC, then ∠CAB is equal to:

(A) 30º
(B) 60º

6. In given figure, if ∠OAB=40º, then ∠ACB is equal to :

(A) 50º
(B) 40º
(C) 60º
(D) 70°

7. In given figure, if ∠DAB=60º, ∠ABD=50º, then ∠ACB is equal to:

(A) 60º
(B) 50º
(C) 70º
(D) 80º

8. ABCD is a cyclic quadrilateral such that AB is a diameter of the circle circumscribing it and

∠ADC=140º, then ∠BAC is equal to:

(A) 80º
(B) 50º

9. In given figure, BC is a diameter of the circle and ∠BAO=60º. Then ∠ADC is equal to :

(A) 30º
(B) 45º

10. In given figure, ∠AOB=90º and ∠ABC=30º, then ∠CAO is equal to:

(A) 30º
(B) 45º
(C) 90º
(D) 60º

11. In given figure, two congruent circles have centres O and O′. Arc AXB subtends an angle of 75º at the centre O and arc A′ Y B′ subtends an angle of 25º at the centre O′. Then the ratio of arcs A X B and A′ Y B′ is:

(A) 2 : 1
(B) 1 : 2
(C) 3 : 1
(D) 1 : 3

12. In given figure, AB and CD are two equal chords of a circle with centre O. OP and OQ are perpendiculars on chords AB and CD, respectively. If ∠POQ=150º, then ∠APQ is equal to

(A) 30º
(B) 75º

ANSWER KEY

1. (D)

2. (A)

3. (C)

4. (B)

5. (D)

6. (A)

7. (C)

8. (B)

9. (C)

10. (D)

11. (C)
12. (B)

Case Study Based Question on Coordinate Geometry

The children of SMPS and DPS are very excited for the football match of inter-school competition, for which the school management has selected the Talkatora football ground and made the booking, as shown in picture below.

The length of the stadium is 120 metres and breadth Is 90 metres. If centre spot is considered as origin, then answer the following questions:

(i) What are the coordinates at which the centre circle meets the halfway line? [1 Mark]

(ii) What will be the coordinates of a player standing 22m away from Centre spot on the straight line joining centre spot to the penalty spot towards the right side goal? [1 Mark]

(iii) What will be the coordinates of the four corners of the football ground? [2 Marks]

What will be the coordinates of the penalty spots of both the goals? [2 Marks]

Solution :

(i) (0, 9.15), (0,-9.15)

(ii) (22,0)

(iii) (60,45), (60, -45), (-60,45) and (-60,-45)

(49,0) and (-49,0)

If a=√[6-√11] and b=√[6+√11] then . . .

Question : If a=√[6-√11] and b=√[6+√11] then the value of (a+b) is :

(a) √22

(b) 2√11

(d) √12

Doubt by Veer

Solution : Coming Soon

Answer : (a) √22

Factories x4+x2+1 . . .

Questin : Factories x⁴+x²+1

Doubt by Veer

Solution :
x⁴+x²+1
Adding x² and subtracting x²
=x⁴+x²+1+x²-x²
=x⁴+x²+x²+1-x²
=x⁴+2x²+1-x²
=[x⁴+2x²+1]-x²
=[(x²)²+2(x²)(1)+(1)²]-x²
=[(x²+1)²-x²] [∵a²+2ab+b²=(a+b)²]
=(x²+1-x)(x²+1+x)
=(x²-x+1)(x²+x+1)

If a2-2a-1=0, then find the value of aa+1/a2 . . .

Question : If a²-2a-1=0, then find the value of a²+1/a²?

Doubt by veer

Solution :

a²-2a-1=0

dividing both sides by a
(a²-2a-1)/a=0/a
a²/a-2a/a-1/a=0/a
a-2-1/a=0
a-1/a=2
S.B.S.
(a-1/a)²=(2)²
(a)²+(1/a)²-2(a)(1/a)=4 [∵(x-y)²=x²+y²-2xy]
a²+1/a²-2=4
a²+1/a²=4+2
a²+1/a²=6

ABCD is a cyclic quadrilateral as shown in the figure . . .

Question : ABCD is a cyclic quadrilateral as shown in the figure. Find the value of (x+y).

Doubt by Purvi

Solution : Coming Soon.

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