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BASIC NUMBERS MCQs

Total Questions : 20 | Page 2 of 2 pages
Question 11.


Find the remainder when 10100 is divided by 7


  1.     4
  2.     3
  3.     2
  4.     -1
  5.     none of these
 Discuss Question
Answer: Option A. -> 4
:
A
Option (a)
Euler's number of 7 ( a prime number) is 71=6. make the numerator power the nearest
multiple of 6. The question changes to
10967R×1047R
part a will yield a remainder 1 and 1047R can be found using frequency method
1017R=3
1027R=2
1037R=67R=1
1047R=47R=4
answer = option a
Question 12.


How many numbers are there from 1 to 1000 which when successively divided by 5, 6, 7 give remainders 2,4,5.


  1.     1
  2.     3
  3.     4
  4.     6
  5.     5
 Discuss Question
Answer: Option C. -> 4
:
C

option c


The first number in this AP can be found as given above


How Many Numbers Are There From 1 To 1000 Which When Success...


The first term = ((((5*6) +4)*5) + 2


Common difference = 5*6*7=210


General form of the AP  is therefore 172+210k,


So the numbers will be 172, 382,592 and 802


Question 13.


Find the least number with 32 factors and at most 3 prime factors?


  1.     1920
  2.     2733
  3.     1080
  4.     582
  5.     none of these
 Discuss Question
Answer: Option C. -> 1080
:
C

option (c)


Let the prime factors be abc


Ways of writing


a31 least value =231


ab15 least value =2153


a3b7 least value =2733


ab3c3 least value =23335=1080


ab7c least value =273151=1920


Question 14.


Find the remainder when (42)442is divided by 100


  1.     24
  2.     34
  3.     44
  4.     64
  5.     74
 Discuss Question
Answer: Option D. -> 64
:
D

option (d)


Using the last two digits technique


(42)442=(21×2)442


=(21)442×(2)442=(21)442×(244)10×22=__41×__76×__04=__41×__04=__64. Option (d)


Question 15.


A 32-digit number has all 9’s. Find the remainder when the number is divided by 111.


  1.     9
  2.     11
  3.     1
  4.     99
  5.     none of these
 Discuss Question
Answer: Option D. -> 99
:
D

option d


Any number of the form aaa (3 digits) or aaaaaa (multiple of 3 digits, i.e. 6, 9 .....) is divisible by 111


Therefore group the above numbers into groups of 3 or multiples of 3.


A 32 digit number can be broken up as (3*10 digits) + (2 digits). The first part is divisible by 111. the last two digits will thus be the remainder = 99


Question 16.


Find the remainder when 1736 is divided by 36?


  1.     0
  2.     1
  3.     -1
  4.     17
  5.     2
 Discuss Question
Answer: Option B. -> 1
:
B

Answer=b


Approach 1


Go by frequency method


1736 gives a remainder =17


17236 gives a remainder =1


Frequency =2


Odd powers remainder =17, even powers =1


Approach 2


Euler’s number of 36 is 36×12×23=12


36=12k. hence, from Fermat theorem 173636|R=1


Note :
Euler's number is the number of co_primes of number which is less than that number.
A number N can be written as ambn (where a and b are the prime factors of N)
eg) 20=22×51
Here a=2 and b=5, m=2 and n=1
Euler's number =N[1(1a)][1(1b)]
From fermat Theorem
N(Eulers number of y+k)yR=1 (i.e When a number N is raised to the Euler's number of a number)
"y" is divided by "y", the remainder will be 1


Question 17.


N=9876543298765432.........82 digits. Find the remainder when N is divided by 34?


  1.     0
  2.     1
  3.     15
  4.     30
  5.     -1
 Discuss Question
Answer: Option D. -> 30
:
D

option d


Use Divisibility Rules


34 = 17 *2


So we should use the divisibility test of 17 ( Compartmentalization method - taking 8 digits at a time (Sum of digits at odd places taken 8 at a time- Sum of digits at even places taken 8 at a time)


Combine 8 digits together, 9876......80 digits*100 + 98 :


There will be equal number of groups (of 8 digits taken at a time) at odd places and even


Places in 9876.......80 digits*100.


So Sum of groups at odd places - Sum of groups at even places = 0


Therefore first part is divisible by 17. It is also divisible by 2, as 100 is divisible by 2.Hence, we only need to find the remainder when 98 is divided by 34


Remainder= 30


Question 18.


Find the last two digits of 71 + 72 + 73 +……………..7342 ?


  1.     07
  2.     01
  3.     49
  4.     43
  5.     56
 Discuss Question
Answer: Option E. -> 56
:
E

option (e)


71=0775=07


72=4976=49


73=4377=43


74=0178=01


There is a cyclicity of 4 as 07, 49 , 43 ,01 is the last 2 digits for the powers of 7


Here 342=4k+2Required answer is 07+49=56


Question 19.


Solve for x
x=1+13+12+13+12+....


  1.     5017
  2.     1017
  3.     3014
  4.     2517
  5.     2
 Discuss Question
Answer: Option D. -> 2517
:
D

1+13=43=1.333. the value of x will be slightly lesser than 1.333 as the denominator keeps increasing


Look at the options


Option a=51.7>2 .this can never be the answer


Option b=11.7<1. this also can never be the answer


Option c=31.4>2. this cannot be the answer


Option d=2.51.7 which is the correct answer


Option e=2, which can never be the answer


Question 20.


What are the last two digits of 47523 ?


  1.     25
  2.     50
  3.     75
  4.     85
  5.     None of these
 Discuss Question
Answer: Option C. -> 75
:
C

option (c )


A number ending in 5, with the tens digit an odd number and raised to an odd power, will


always end with 75. Answer is option (c)


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