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19 Sep 2019, 03:53
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A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
85%
(hard)
Question Stats:
38% (01:28) correct
62%
(01:24)
wrong
based on 186
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Time
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Which of the following is a perfect square?
A. 79,242,972,893,648,656
B. 9,134,751,098,236,810
C. 5,916,378,240,699,596
D. 2.893,467,827,688,677
E. None of the above
A. 79,242,972,893,648,656
B. 9,134,751,098,236,810
C. 5,916,378,240,699,596
D. 2.893,467,827,688,677
E. None of the above
which of these is a perfect square?
A) 2893467827688677
B) 79242972893648656
C) 9134751098236810
D) 5916378240699596
E) None of the above
A) 2893467827688677
B) 79242972893648656
C) 9134751098236810
D) 5916378240699596
E) None of the above
19 Sep 2019, 05:31
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We can eliminate B directly as it has only 1(odd) trailing 0, and eliminate D, as no number that has unit digit 7 is perfect square.
Add the digits of the option A and C to single digit, if we get 1, 4, 7 or 9 it's can be a perfect square.
7+9+2+4+2+9+7+2+8+9+3+6+4+8+6+5+6 = 9+7= 1+6=7 (Keep A)
5+9+1+6+3+7+8+2+4+0+6+9+9+5+9+6=8+9=1+7=8 (Eliminate C)
Just to make sure that A is a perfect square, I actually calculate the the square root of this number with traditional method and i got a positive integer.
A
Add the digits of the option A and C to single digit, if we get 1, 4, 7 or 9 it's can be a perfect square.
7+9+2+4+2+9+7+2+8+9+3+6+4+8+6+5+6 = 9+7= 1+6=7 (Keep A)
5+9+1+6+3+7+8+2+4+0+6+9+9+5+9+6=8+9=1+7=8 (Eliminate C)
Just to make sure that A is a perfect square, I actually calculate the the square root of this number with traditional method and i got a positive integer.
A
Bunuel
Archit3110
19 Sep 2019, 08:39
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Perfect square can have following as units digits; 1,4,9,6,5& atleast one 0
from given options we can say that options D & B are clearly out
Amongst A & C one additional observation is that whenever we have units digit as 6 the tens digit would be odd here both options have an odd integer
so the only way now left to check whether no is a perfect square or not is by digital sum method; viz sum of all individual digits of no. if we get 1, 4, 7 or 9 it's can be a perfect square.
79,242,972,893,648,656= 97; 16 ; 1+6 ; 7
5,916,378,240,699,596=89; 17;1+8 ; 8
IMO A ; is valid
Bunuel ; is the given answer option correct? how can it be E?
[quote="Bunuel"]Which of the following is a perfect square?
A. 79,242,972,893,648,656
B. 9,134,751,098,236,810
C. 5,916,378,240,699,596
D. 2.893,467,827,688,677
E. None of the above
from given options we can say that options D & B are clearly out
Amongst A & C one additional observation is that whenever we have units digit as 6 the tens digit would be odd here both options have an odd integer
so the only way now left to check whether no is a perfect square or not is by digital sum method; viz sum of all individual digits of no. if we get 1, 4, 7 or 9 it's can be a perfect square.
79,242,972,893,648,656= 97; 16 ; 1+6 ; 7
5,916,378,240,699,596=89; 17;1+8 ; 8
IMO A ; is valid
Bunuel ; is the given answer option correct? how can it be E?
[quote="Bunuel"]Which of the following is a perfect square?
A. 79,242,972,893,648,656
B. 9,134,751,098,236,810
C. 5,916,378,240,699,596
D. 2.893,467,827,688,677
E. None of the above
