Directions (46-47): Read the following quadric equation carefully and answer the questions given below.
Equation 1:
Equation 2:
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’ .
Correct Answer :
12
Solution :
To find the value of , let us analyze the given conditions step-by-step:
Step 1: Determine the value of
According to Note (i), is a single-digit prime number greater than 2.
The single-digit prime numbers are 2, 3, 5, and 7. Since , must be one of .
According to Note (viii), , or .
Step 2: Determine the values of and
According to Note (ii), and 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), . Thus, must be one of .
According to Note (iv), . This gives us the following possible pairs for :
1. If , then can be 17 or 19.
2. If , then can only be 19.
3. If , there is no prime less than 20 greater than .
Now, let us use the condition :
Since the minimum possible value for is 17, we must have .
Out of the candidates , only satisfies this inequality.
Thus, we must have .
Step 3: Analyze Equation 2 to find , , and the roots
Equation 2 is given by:
According to Note (vii), .
Since no root is irrational (Note vi), the discriminant of Equation 2, , must be a perfect square.
Let us test the possible configurations for with :
- Case A: , :
Here, .
The discriminant is (negative, hence imaginary roots). This case is invalid.
- Case B: , :
Here, .
The discriminant is (negative, hence imaginary roots). This case is invalid.
- Case C: , :
Here, .
The discriminant is .
Since 36 is a perfect square (), this configuration is valid. The roots of Equation 2 are:
The two roots are:
The smallest root of Equation 2 is .
Step 4: Find the value of 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 .
Substituting into Equation 1:
Substitute the known values and :
.
The correct option corresponding to this value is 12.
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