Question Details

Directions (46-47): Read the following quadric equation carefully and answer the questions given below.

Equation 1: ax2+bx+c=0
Equation 2: dy2+ey+c=0

Note:
(i) c is a single digit prime number greater than 2
(ii) d and b are two digits prime number less than 20
(iii) d is greater than 11
(iv) b is greater than d
(v) Smallest roots of both the equation are same
(vi) No root is irrational
(vii) e = b + 1
(viii) 3c is greater than b

Find the value of ‘a’ .

Options

A

13

B

14

C

12

D

10

E

15

Show Answer

Correct Answer :

Option C

12

12

Solution :

To find the value of a, let us analyze the given conditions step-by-step:

Step 1: Determine the value of c
According to Note (i), c is a single-digit prime number greater than 2.
The single-digit prime numbers are 2, 3, 5, and 7. Since c>2, c must be one of {3,5,7}.
According to Note (viii), 3c>b, or c>b3.

Step 2: Determine the values of d and b
According to Note (ii), d and b are two-digit prime numbers less than 20.
The two-digit prime numbers less than 20 are 11, 13, 17, and 19.
According to Note (iii), d>11. Thus, d must be one of {13,17,19}.
According to Note (iv), b>d. This gives us the following possible pairs for (d,b):
1. If d=13, then b can be 17 or 19.
2. If d=17, then b can only be 19.
3. If d=19, there is no prime less than 20 greater than d.

Now, let us use the condition 3c>b:
Since the minimum possible value for b is 17, we must have 3c>17c>5.67.
Out of the candidates {3,5,7}, only c=7 satisfies this inequality.
Thus, we must have c=7.

Step 3: Analyze Equation 2 to find d, b, and the roots
Equation 2 is given by:
dy2+ey+c=0
According to Note (vii), e=b+1.
Since no root is irrational (Note vi), the discriminant of Equation 2, D=e2-4dc, must be a perfect square.

Let us test the possible configurations for (d,b) with c=7:
- Case A: d=13, b=17:
Here, e=17+1=18.
The discriminant is D=182-4(13)(7)=324-364=-40 (negative, hence imaginary roots). This case is invalid.

- Case B: d=17, b=19:
Here, e=19+1=20.
The discriminant is D=202-4(17)(7)=400-476=-76 (negative, hence imaginary roots). This case is invalid.

- Case C: d=13, b=19:
Here, e=19+1=20.
The discriminant is D=202-4(13)(7)=400-364=36.
Since 36 is a perfect square (62), this configuration is valid. The roots of Equation 2 are:
y=-20±362(13)=-20±626
The two roots are:
y1=-20-626=-1
y2=-20+626=-713
The smallest root of Equation 2 is -1.

Step 4: Find the value of a using Equation 1
According to Note (v), the smallest roots of both equations are the same. Thus, the smallest root of Equation 1 is also -1.
Substituting x=-1 into Equation 1:
ax2+bx+c=0
a(-1)2+b(-1)+c=0
a-b+c=0
Substitute the known values b=19 and c=7:
a-19+7=0
a-12=0a=12.

The correct option corresponding to this value is 12.

Unlock Our Free Library

Access expert-curated educational resources and study materials—completely free.

Discover more resources

You may also like

Mock Tests

View All
  • CTET
  • intermediate
  • No time limit
  • child development and pedagogy, mathematics, social science

  • SSC
  • intermediate
  • 2 hours and 30 mins
  • child development and pedagogy, mathematics, social science

Ask AI Tutor
5 left
Q1 View Question & Options
AI Tutor is solving this question...
Reading question context & options...