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May 6, 2019

I.S.I B.Stat Paper 2019 Subjective| problems & solutions

Here, you will find all the questions of ISI Entrance Paper 2019 from Indian Statistical Institute's B.Stat Entrance. You will also get the solutions soon of all the previous year problems.

Problem 1:

Prove that the positive integers $n$ that cannot be written as a sum of $r$ consecutive positive integers, with $r>1$, are of the form $n=2^{l}$ for some $l \geq 0$.

Problem 2:

Let $f:(0, \infty) \rightarrow \mathbb{R}$ be defined by
$$
f(x)=\lim _{n \rightarrow \infty} \cos ^{n}\left(\frac{1}{n^{x}}\right)
$$
(a) Show that $f$ has exactly one point of discontinuity.
(b) Evaluate $f$ at its point of discontinuity.

Problem 3:

Let $\Omega={z=x+i y \in \mathbf{C}:|y| \leq 1} .$ If $f(z)=z^{2}+2,$ then draw a
sketch of
$$
f(\Omega)={f(z): z \in \Omega}
$$
Justify your answer.

Problem 4:

Let $f: \mathbf{R} \rightarrow \mathbf{R}$ be a twice differentiable function such that
$$
\frac{1}{2 y} \int_{x-y}^{x+y} f(t) d t=f(x), \quad \text { for all } x \in \mathbf{R}, y>0
$$
Show that there exist $a, b \in \mathbf{R}$ such that $f(x)=a x+b$ for all $x \in \mathbb{R}$

Problem 5:

A subset $S$ of the plane is called convex if given any two points $x$ and $y$ in $S,$ the line segment joining $x$ and $y$ is contained in $S .$ A quadrilateral is called convex if the region enclosed by the edges of the quadrilateral is a convex set.

Show that given a convex quadrilateral $Q$ of area $1,$ there is a rectangle $R$ of area 2 such that $Q$ can be drawn inside $R$.

Problem 6:

For all natural numbers $n$, let
$$
A_{n}=\sqrt{2-\sqrt{2+\sqrt{2+\cdots+\sqrt{2}}}}(n \text { many radicals })
$$
(a) Show that for $n \geq 2$.
$$
A_{n}=2 \sin \frac{\pi}{2^{n+1}}
$$
(b) Hence, or otherwise, evaluate the limit
$\lim_{n \to \infty} 2^{n}A_{n}$

Problem 7:

Let $f$ be a polynomial with integer coefficients. Define
$$
a_{1}=f(0), a_{2}=f\left(a_{1}\right)=f(f(0))
$$
and
$$
a_{n}=f\left(a_{n-1}\right) \quad \text { for } n \geq 3
$$
If there exists a natural number $k \geq 3$ such that $a_{k}=0,$ then prove that either $a_{1}=0$ or $a_{2}=0$.

Problem 8:

Consider the following subsets of the plane:
$C_{1}=\{(x, y): x>0, y=\frac{1}{x}\}$
and
$C_{2}=\{(x, y): x<0, y=-1+\frac{1}{x}\}$
Given any two points $P=(x, y)$ and $Q=(u, v)$ of the plane, their distance $d(P, Q)$ is defined by
$$
d(P, Q)=\sqrt{(x-u)^{2}+(y-v)^{2}}
$$
Show that there exists a unique choice of points $P_{0} \in C_{1}$ and $Q_{0} \in C_{2}$ such that
$d\left(P_{0}, Q_{0}\right) \leq d(P, Q)$ for all $P \in C_{1}$ and $Q \in C_{2}$

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37 comments on “I.S.I B.Stat Paper 2019 Subjective| problems & solutions”

  1. In the third question the area of the resultant polygon is 2/3rd of the area of the triangle
    Area = 2/3 x 9√3/2
    = 3√3
    The answer is option d

  2. 16th Question the right answer should be 33 , it's not such an easy case of PHP as it seems like, for that we have to calculate
    Number of Student who visited 5 days- 5C5=1
    Number of Student who visited 4 days- 5C4=5
    Number of Student who visited 3 days- 5C3=10
    Number of Student who visited 2 days- 5C2=10
    Number of Student who visited 1 day - 5C1=5
    Number of Student who visited 0 day - 5C0=1
    Total 32 cases, now applying Pigeon Hole Principle we need 33 students

  3. For objective #16, if we represent the days visited as a YES/NO tuple of (a1,a2,...,a5), then for each student, 2^5=32 such tuples are possible. So, there are 32 boxes and so the minimum number of students needed to guarantee the condition (in question) has to be 33. So answer should be (C)33.

      1. 18's correct option should be A.Let's assume we sent two children together, one children alone and both adults separately then we found that the boat has to cross the river 9 times

  4. In ques. 19, for adults it would be 4 times(2 for each) and for 2 children 2 times and as it is written no adult so 'max'... So for last 1 children, 2 times so total 4+2+2=8.. Sir please tell options are true.

      1. they have told m are integer's' and n is not equal to zero which includes all real numbers
        they haven't specifically said that values n are also are integers

        1. I hope that works out. However, usually, when mathematicians say integers m and n not 0, they usually mean both m and n are integers and n is not 0. Anyway, maybe your answer is correct. We have posted unofficial options.

  5. for the 11th march to 15th march question,why should we consider not swimming on any dates as a possibility ?The empty set should not be considered,since we are asked to figure out whether they 'swim' on the same dates.Not swimming at all shouldn't be an option.

  6. I gave ISI BMath 2019 and scored 93 in UGA, And in UGB I attempted total 6 questions,3 questions correctly with 2 being partially answered and one being fully wrong, I am OBC too, Will I be called for the interview?

      1. but the one i did wrong was the first question.... is it something dangerous.... i mean about the impression to the checker?

  7. Correct option of question no. 19 should be D. We can get 3 also there from the determinant.

  8. HOW DID YOU GET THE SOLUTION FOR Q.26 ?

    I COULD NOT FIND ANY SOLUTION SO I THINK ANSWER WILL BE 0 i.e (A).

    IF YOU GET 1 SOLUTION STISFYING THE CONDITION THEN FOR WHAT VALUE OF n IS IT FOR?

  9. sir #16 will be (b) 1
    as the slope of e^x is always > any polynomial function.it only cut once in the 2nd quadrant.

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