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.  SOLUTION TO NTPC PLACEMENT PAPER. GENERAL APTITUDE QUESTIONS: 1 The expression (11.98 x 11.98 + 11.98 x x + 0.02 x 0.02) will be a perfect square for x equal to:  Answer: Option C Explanation: Given expression = (11.98)^{2} + (0.02)^{2} + 11.98 x x. For the given expression to be a perfect square, we must have 11.98 x x = 2 x 11.98 x 0.02 or x = 0.04 
2.  Simple interest on a certain sum of money for 3 years at 8% per annum is half the compound interest on Rs. 4000 for 2 years at 10% per annum. The sum placed on simple interest is:  Answer: Option C Explanation: C.I.  = Rs.   4000 x   1 +  10   2  – 4000   100 
  = Rs.   4000 x  11  x  11  – 4000   10  10 
  = Rs. 840. 
Sum = Rs.   420 x 100   = Rs. 1750.  3 x 8 

3.  A boat running downstream covers a distance of 16 km in 2 hours while for covering the same distance upstream, it takes 4 hours. What is the speed of the boat in still water?  Answer: Option B Explanation: Rate downstream =   16  kmph = 8 kmph.  2 
Rate upstream =   16  kmph = 4 kmph.  4 
Speed in still water =  1  (8 + 4) kmph = 6 kmph.  2 

4.  A large tanker can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half?  Answer: Option D Explanation: Part filled by (A + B) in 1 minute =   1  +  1   =  1  .  60  40  24 
Suppose the tank is filled in x minutes. x = 30 min. 
5 .  Out of 7 consonants and 4 vowels, how many words of 3 consonants and 2 vowels can be formed?  Answer: Option C Explanation: Number of ways of selecting (3 consonants out of 7) and (2 vowels out of 4)  = (^{7}C_{3} x ^{4}C_{2})   =   7 x 6 x 5  x  4 x 3   3 x 2 x 1  2 x 1 
  = 210. 
Number of groups, each having 3 consonants and 2 vowels = 210. Each group contains 5 letters. Number of ways of arranging
5 letters among themselves  = 5!   = 5 x 4 x 3 x 2 x 1   = 120. 
Required number of ways = (210 x 120) = 25200 . TECHNICAL QUESTIONS: 
 
2.  If 750 µA is flowing through 11 k of resistance, what is the voltage drop across the resistor? 

3.  At the end of a 14 day period, your utility bill shows that you have used 18 kWh. What is your average daily power? 
Answer: Option A 
4.  A halfwatt is equal to how many milliwatts? 
Answer: Option C 
5.  Series aiding is a term sometimes used to describe voltage sources of the same polarity in series. 
Answer: Option A 
6.  If there are a total of 120 mA into a parallel circuit consisting of three branches, and two of the branch currents are 40 mA and 10 mA, the third branch current is 
Answer: Option B 
7.  In a parallel circuit, the branch with the lowest resistance has the most current. 
Answer: Option A 
11.  Thirdorder determinants are evaluated by the expansion method or by the cofactor method. 
Answer: Option A 
12.  A 2 F, a 4 F, and a 10 F capacitor are connected in series. The total capacitance is less than 
Answer: Option D 
13.  Five time constants are required for a capacitor to charge fully or discharge fully. 
Answer: Option A 
14.  In an RL circuit, the impedance is determined by both the resistance and the inductive reactance combined. 
Answer: Option A 
15.  A 10 resistor, a 90 mH coil, and a 0.015 F capacitor are in series across an ac source. The impedance magnitude at 1,200 Hz below f_{r} is 
Answer: Option A 
16.  A certain series RLC circuit with a 200 Hz, 15 V ac source has the following values: R = 12 , C = 80 F, and L = 10 mH. The total impedance, expressed in polar form, is 
Answer: Option A 
17.  Referring to Problem 18, what is the bandwidth of the filter? 
Answer: Option D 
18.  In an RC differentiator, the sum of the capacitor voltage and the resistor voltage at any instant 
 A.    B.  must be equal to the applied voltage 
  C.  is less than the applied voltage but greater than zero 
  D.  
Answer: Option B 
19.  If the RC time constant of an integrator is increased, as the time constant is increased 
 A.  the capacitor charges more during a pulse and discharges less between pulses 
  B.  the capacitor charges less during a pulse and discharges more between pulses 
  C.  the capacitor charges more during a pulse and discharges more between pulses 
  D.  the capacitor charges less during a pulse and discharges less between pulses 

Answer: Option D 
20.  In an RL integrating circuit, the output voltage is taken across the inductor. 
Answer: Option B 
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