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Logical Reasoning
Number Series
Q. The units digit of the sum of the first 97 positive integers (that is 1 + 2 + 3 + ... + 97 ) is
Read Solution (Total 22)
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- 433
the sum of all units place of 1 to 9 = 45
so,upto 100 numbers is 45*10=450
then
we havw up to 97 only.....so minus of 8and9 gives 450-17=433 - 11 years agoHelpfull: Yes(25) No(4)
- ans is 3.....
sum of n natural numbers is (n(n+1))/2.so (97*98)/2=97*49...so 9*7=63....so unit digit is 3 - 11 years agoHelpfull: Yes(18) No(3)
- i guess answer is 4753 is it right ?
- 11 years agoHelpfull: Yes(6) No(6)
- 1 + 2 + 3 + ... + 97
then by adding all unit place digits we get 433
then in units place 3 is present - 11 years agoHelpfull: Yes(6) No(2)
- sorry, I didnt read question carefully,units digit =3 because sum=4753
ans=3 - 11 years agoHelpfull: Yes(4) No(2)
- the sum of positive integers=n*(n=1)/2
Here, n=97
Sum=4753 - 11 years agoHelpfull: Yes(2) No(2)
- s=n*(n+1)/2
here, n=97
so, s=4753
unit digit is 3 - 11 years agoHelpfull: Yes(2) No(1)
- sum of the seires =n/2[2a+(n-1)d] ,here n=97 a=1 and d=1 thus value obtained will be 4753 from the formula,here unit digit is 3
- 11 years agoHelpfull: Yes(1) No(0)
- 4753 is rite ans
- 11 years agoHelpfull: Yes(1) No(0)
- 97/2*(1+97)=4753
unit digit=3 - 11 years agoHelpfull: Yes(1) No(1)
- (97*(97+1))/2
4753 - 11 years agoHelpfull: Yes(0) No(1)
- sum=(n*(n+1))/2.
here n=97 s0 n*(n+1)=9506
so sum=4753
units digit=3 - 11 years agoHelpfull: Yes(0) No(0)
- 3 is the ans
- 11 years agoHelpfull: Yes(0) No(1)
- 3 because 9*7 is 63.
- 11 years agoHelpfull: Yes(0) No(2)
- sum of 1-10 gives 45 so unit digit is 5,then 11-20(count for 1-10) unit digit is 5
so up to 8 ie 81-90 it is 45 so unit place is 5.so summing up its 8*5=40 so unit place is 0.then 91 to 97 its 28,add unit places u get 8 ans. - 11 years agoHelpfull: Yes(0) No(2)
- 5
1+2+3+4+5+6+7+8+9+10 - 11 years agoHelpfull: Yes(0) No(0)
- 450-17=433
- 11 years agoHelpfull: Yes(0) No(0)
- unit digit is 3..
- 11 years agoHelpfull: Yes(0) No(1)
- The Answer is 3
- 11 years agoHelpfull: Yes(0) No(0)
- answer is 8.
sum of 1 to 9 = 45
to 90 unit digit will be 0(5+5=10)
sum of 1 to 7 = 28
so, answer is 8. - 10 years agoHelpfull: Yes(0) No(0)
- n(n+1)/2=97(97+1)/2=97(49)=3
- 10 years agoHelpfull: Yes(0) No(1)
- since the given problem is in A.P
common diff=1,and total no.of terms =97
so ,sum is =97(1+97)/2 =97*49
by using remainder method,(97*49)/10 =(7*9)/10 =3
so unit digit of the sum is = 3.
- 10 years agoHelpfull: Yes(0) No(0)
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