13
Q:

In the following question a number series is given which has only one wrong number. You have to find out the wrong number?

7.5  47.5  87.5  157.5  247.5  357.5  487.5 

A) 47.5 B) 87.5
C) 247.5 D) 357.5

Answer:   A) 47.5

Explanation:
Q:

Find the least number with which 16200 should be multiplied, to make it a perfect cube ?

A) 45 B) 48
C) 360 D) 36
 
Answer & Explanation Answer: A) 45

Explanation:

16200 =

A perfect cube has a property of having the indices of all its prime factors divisible by 3.

Required number =  = 9x5 = 45.

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1 39
Q:

Three numbers which are co-prime to each other are such that the product of the first two is 551 and that of the last two is 1073. The sum of the three numbers is :

A) 83 B) 89
C) 85 D) 79
 
Answer & Explanation Answer: C) 85

Explanation:

Since the numbers are co-prime, they contain only 1 as the common factor.
Also, the given two products have the middle number in common.
So, middle number = H.C.F of 551 and 1073 = 29;
First number = 551/29 = 19
Third number = 1073/29 = 37.
Required sum = 19 + 29 + 37 = 85.

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1 11
Q:

The sum of the two digits of a number is 8. If the number is subtracted from the number obtained by reversing its digits, the result is 54. Find the number ?

A) 28 B) 19
C) 37 D) 17
 
Answer & Explanation Answer: D) 17

Explanation:

Any two digit number can be written as (10P + Q), where P is the digit in the tens place and Q is the digit in the units place.
P + Q = 8 ----- (1)
(10Q + P) - (10P + Q) = 54
9(Q - P) = 54
(Q - P) = 6 ----- (2)
Solve (1) and (2) P = 1 and Q = 7
The required number is = 17

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1 10
Q:

The series of differences between consecutive prime numbers is represented as Cp1, Cp2, Cp3, .... Cpn , Whare Cp1 is the difference between the second and the first prime number. Find the sum of series when n = 23, given that the 23rd prime number is 83 ? 

A) 87 B) 81
C) 83 D) 85
 
Answer & Explanation Answer: A) 87

Explanation:

Cp1 = p2 - p1 ,
Cp2 = p3 - p2
..
..
..
Cp23 = p24 - p23
Sum of series = (p2-p1) + (p3-p2) + .....(p23-p22) + (p24-p23)
All terms get cancelled, except p1 = 2 and p24 = 89
So Sum = -p1 + p24
Sum of series = -2 + 89 = 87

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4 13
Q:

Total 100 members are writing exam. In that 48 members are writing first exam, 45 members are writing second exam and 38 members are writing third exam. 5 members are writing all the three exams. How many members are writing 2 exams ?

A) 26 B) 23
C) 27 D) 21
 
Answer & Explanation Answer: D) 21

Explanation:

Total number of exams written by 100 students = 48 + 45 + 38 = 131
Now let us say x members are writing only 1 exam, y members are writing only 2 exams, z members are writing only 3 exams.
Therefore, x + 2y + 3z = 131 also x + y + z = 100.
Given that z = 5. So x + 2y = 116 and x + y = 95.
Solving we get y = 21.
So 21 members are writing exactly 2 exams.

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3 15