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02 Mar 2021, 20:53
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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:
65%
(hard)
Question Stats:
54% (02:03) correct
46%
(01:59)
wrong
based on 175
sessions
History
Date
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Not Attempted Yet
If n is a positive integer, what is the tens' digit of 7^n?
(1) n is divisible by 4.
(2) n is divisible by 3.
(1) n is divisible by 4.
(2) n is divisible by 3.
02 Mar 2021, 22:30
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akshayuberoi
In actual, the questions may stick to units digit only, because the tens digit, as in this question, would just involve intensive calculations and no technique.
If a question has been asked for units digit or tens digit, more often than not, you will get your answer by finding pattern.
\(7^0=01\)
\(7^1=07\)
\(7^2=49\)
\(7^3=343\) or 43
\(7^5=43*7\)=301 or 01
\(7^6=01*7=07\)
......
Thus the last two digits are cyclic after every 4 terms => 07, 49, 43, 01, 07......
Pattern of units digit => 7, 9, 3, 1, 7...
Pattern of tens digit => 0, 4, 4, 0 ...
(1) n is divisible by 4.
So the tens digit will be 0
Sufficient
(2) n is divisible by 3.
If it is 3, then it is 4. But if it is 9, that is 4*2+1, the tens digits will be 0.
Insufficient
A
23 May 2023, 01:20
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For those who read Ten's digit as Unit's digit. I feel for you. You and I are on the same boat. Keep up the grind!
