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X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit
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08 Feb 2016, 17:45
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X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit of X102? A. 3 B. 5 C. 8 D. 11 E. 15 Attachment:
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Re: X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit
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08 Feb 2016, 19:30
MathRevolution wrote: X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit of X102? A. 3 B. 5 C. 8 D. 11 E. 15 Attachment: X1=1.jpg * A solution will be posted in two days. X1 = 1 x2 = 1+7*1 = 8 X3 = 1+7*8 = 57 X4 = 1+7*57 = 400 From this we can see for all even X the unit digit is even and for Odd it is Odd. From the answer choices only C is even hence that is the correct choice.



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Re: X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit
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08 Feb 2016, 20:04
ankushjain wrote: MathRevolution wrote: X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit of X102? A. 3 B. 5 C. 8 D. 11 E. 15 Attachment: X1=1.jpg * A solution will be posted in two days. X1 = 1 x2 = 1+7*1 = 8 X3 = 1+7*8 = 57 X4 = 1+7*57 = 400 From this we can see for all even X the unit digit is even and for Odd it is Odd. From the answer choices only C is even hence that is the correct choice. hi ankush, if there was a choice as 0 or 4 also, then what would you have done.. you have to look for patterns in these Qs..if you check for x5 it will be 1, since x4 had a 0 in units digit.. and thereafter ti will keep following the pattern.. 1,8,7,0,1,8,7,0.. repetition is after every 4th number..102= 4*25 + 2.. so it will have the same units digit as the second number, which is 8..
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Re: X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit
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10 Feb 2016, 20:55
X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit of X102? A. 3 B. 5 C. 8 D. 11 E. 15 > When substituting, it becomes X1=1, X2=~8, X3=~7. X4=~0, X5=~1. That is, 1 > 8 > 7 > 0 > 1.. are repeated every 4 cycle. Thus, X102=X4*25+2 > X2=~8 and the answer is C.
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Re: X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit
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16 Feb 2016, 02:04
Xn=1+7Xn1
So when n=1, X1 = 1 + 7X(11) = 1 (which is true per question) therefore X0=0. when n=2, X2 = 1 + 7X(21) = 1 + 7X1 = 1 + 7(1) = 8 (here we know X1 = 1 from the previous step).
Whatever value N may be, the value of X(n1) is less than 1.
If N =102, then X(n1) = 101.
Substituting in the equation, X102 = 1 + 7(101) = 1 + 707 = 708.



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Re: X1=1, for all positive integers, Xn=1+7Xn1 , what is the units digit
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01 Aug 2018, 08:41
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