# 12th Maths Paper Solutions Set 1 : CBSE Delhi Previous Year 2005

General Instructions:
(i) The question paper consists of three sections A, B and C Section A is compulsory for all students. In addition to Section A, every student has to attempt either Section B OR Section C.
(ii) For Section A -
Question numbers 1 to 8 are of 3 marks each.
Question numbers 9 to 15 are of 4 marks each.
Question numbers 16 to 18 are of 6 marks each.<o:p></o:p></span></p>
(iii) For Section B/Section C
Question numbers 19 to 22 are of 3 marks each.
Question numbers 23 to 25 are of 4 marks each.
Question number 26 is of 6 marks.
(iv) All questions are compulsory.
(v) Internal choices have been provided in some questions. You have to attempt only one of the choices in such questions.
(vi) Use of calculator is not permitted. However, you may ask for logarithmic and statistical tables, if required.
Q1 :

If, prove that A3 -4A2+ A= O.

We have

Hence, A3 -4A2+ A= O

Q2 :

Show that, where a, band care in A.P.

Now, the given determinant is

By applying R2 â†’R2- R1and R3 â†’R3- R2, we have

Q3 :

In a single throw of three dice, determine the probability of getting

1. a total of 5

2. a total of at most 5

When three dice are thrown once, the total number of favourable outcomes are (6)3.

1. In a single throw of three dice, we can get a total of 5 in the following ways.

(1, 1, 3), (1, 3, 1), (3, 1, 1), (1, 2, 2), (2, 1, 2), (2, 2, 1)

1. In a single throw of three dice, we can get a total of at most 5 in the following ways.

(1, 1, 1), (1, 1, 2), (1, 2, 1), (2, 1, 1), (1, 1, 3), (1, 3, 1), (3, 1, 1), (1, 2, 2), (2, 1, 2), (2, 2, 1)

Q4 :

A class consists of 10 boys and 8 girls. Three students are selected at random. Find theprobability that the selected group has

(a) all boys,

(b) all girls,

(c) 2 boys and 1 girl.

Q5 :

Evaluate:

Q6 :

Evaluate:

Q7 :

Form the differential equation representing the family y2 2ay + x2= a2, where ais an arbitrary constant.

Q8 :

Solve the following differential equation:

Or

Solve the following differential equation:

Q9 :

Prove that: p â†” q â‰¡(p q) âˆ¨(q p)

Or

Test the validity of the following argument:

S1: p âˆ§ q

S2: âˆ¼ p

S: q

Q10 :

Evaluate:

Q11 :

Differentiate w.r.t. xfrom first principles.

Q12 :

If and, find .

Q13 :

The surface area of a spherical bubble is increasing at the rate of 2 cm2/sec. Find the rate at which the volume of the bubble is increasing at the instant its radius is 6 cm.

Q14 :

Evaluate:

Q15 :

Evaluate:

Q16 :

Using matrices solve the following system of linear equations:

Or

If, find xand ysuch that. Hence, find.

Q17 :

A wire of length 36 cm is cut into two pieces. One of the pieces is turned in the form of a square and the other in the form of an equilateral triangle. Find the length of each piece so that the sum of the areas of the two be minimum.

Q18 :

Find the area boundby the curve and the straight line

Q19 :

Express the vector as the sum of two vectors such that one is parallel to the vector and the other is perpendicular to .

Q20 :

If the vectors , and be coplanar, show that c2= ab.

Q21 :

A car, travelling with a uniform acceleration, has a velocity of 18 km/hour at a certain time and 54 km/hour after covering a distance of 500 m. How much further will it travel to attain a velocity of 72 km/hour?

Out of current syllabus

Q22 :

Abody falls freely from the top of a tower. It covers of the whole distance in the last second. Find the height of the tower and the total time taken by the body to fall down.

Out of current syllabus

Or

A cricket ball is projected with a velocity of 29.4 m/sec. Find

(a) The greatest range on the horizontal plane; and

(b) The angle of projection to give a range of 44.10 m.

Out of current syllabus

Q23 :

Find the co-ordinates of the foot of the perpendicular drawn from the point A(1, 8, 4) to the line joining the points B (0, −1, 3) and C (2, −3, −1).

Q24 :

The resultant of two forces and acting at a point is at right angle to force . While the resultant of forces and acting at the same angle, is at right angle to force. Prove that .

Out of current syllabus

Q25 :

and are two unlike parallel forces. When the magnitude of is doubled, it is found that the line of action of is midway between the lines of action of the new and original resultants. Find the ratio of Pand Q

Out of current syllabus

Or

Three forces acting on a particle are in equilibrium. If the angle between the first force and the second force be 120Â°and that between the second force and the third force be 135Â°, find the ratio of their magnitudes.

Out of current syllabus

Q26 :

Find the Cartesian as well as the vector equation of the planes passing through the intersection of the planes

and , which are at unit distance from the origin.

Q27 :

Solve the following linear programming problem graphically:

Maximise z = 60x+ 15y

Subjectto the constraints

x+ y â‰¤50

3x+ y â‰¤90

x, y â‰¥0.

Q28 :

Two tailors A and B earn Rs.150 and Rs.200 per day respectively. A can stitch 6 shirts and 4 pants per day while B can stitch 10 shirts and 4 pants per day. Form a linear programming problem to minimise the labour cost to produce at least 60 shirts and 32 pants.

Q29 :

A company has two plants to manufacture motor cycles. 70% motor cycles are manufactured at the first plant, while 30% are manufactured at the second plant. At the first plant, 80% motor cycles are rated of the standard quality while at the second plant, 90% are rated of standard quality. A motor cycle, randomly picked up, is found to be of standard quality. Find the probability that it has come out from the second plant.

Q30 :

The probability that a student entering a university will graduate is 0.4. Find the probability that out of 3 students of the university:
(a) None will graduate,
(b) Only one will graduate,
(c) All will graduate.

Or

In a book of 200 pages, 200 misprints are randomly distributed. Using Poisson's distribution, calculate the probability that a randomly observed page of the book will be found to have at least 3 errors. [Use: e1=0.3679]

Q31 :

A, B and C are engaged in a printing business. A being the working partner, receives 10% of the net profit as salary. The remaining profit is divided among themselves in the ratio 4: 5 : 9. If A gets in total Rs. 300000, find the total profit in the business and the shares of B and C in it.

Or

A and B are partners in a business sharing profits and losses equally. They admit a new partner C and it is agreed that now the profits and losses will be shared amongst A, B and C in the ratio 9 : 8 : 7 respectively. If C paid Rs. 2.10 lakh as premium for the goodwill, find the shares of A and B in the premium.

Q32 :

Find the present worth of an ordinary annuity of Rs. 1200 per annum for 10 years at 12% per annum, compounded annually. [Use (1.12) 10= 0.3221]

Q33 :

A calculator manufacturing company finds that the daily cost of producing xcalculators is given by C(x) = 200x+ 7500.
(a) If each calculator is sold for Rs 350, find the minimum number of calculators that must be produced daily and sold to ensure no loss.

(b) If the selling price is increased by Rs 150, what would be the break-even point?