While calculating the average of eight 2-digit numbers, a student mist
| While calculating the average of eight 2-digit numbers, a student mistakenly interchanged the digits of a number as a result the average becomes 9 less than the original average. What is the difference of two digit of that number?
A. 6
B. 7
C. 4
D. 8
Right Answer is: D
SOLUTION
Let the unit and tenth digit of the original number is y and x respectively. Then, the original number is (10x+y) and interchanged digit number is (10y+x). Let the sum of remaining seven numbers is S and the original average is A. Then,
S+(10x+y)=8A……(i)
and
S+(10y+x)=8(A-9)
S+(10y+x)=8A-72……(ii)
Subtracting second from first we get
10x+y-10y-x=72
9x-9y=72
x-y=8
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While calculating the average of eight 2-digit numbers, a student mist