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# A sequence 1, 2, 3, 4. What is the tens' digit of the sum of

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Senior Manager
Joined: 08 Aug 2005
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Kudos [?]: 19 [0], given: 0

A sequence 1, 2, 3, 4. What is the tens' digit of the sum of [#permalink]  09 Aug 2006, 00:47
A sequence 1, 2, 3, 4. What is the tens' digit of the sum of first forty terms?
Senior Manager
Joined: 19 Jul 2006
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Kudos [?]: 3 [0], given: 0

sum = n(n+1)/2 = 40*41/2 = 820
Senior Manager
Joined: 14 Jul 2005
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Kudos [?]: 12 [0], given: 0

agree with AK 2 it is !
Manager
Joined: 20 Mar 2006
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Kudos [?]: 1 [0], given: 0

Re: Sequence [#permalink]  13 Aug 2006, 16:22
getzgetzu wrote:
A sequence 1, 2, 3, 4. What is the tens' digit of the sum of first forty terms?

is the Q 1+2+3+4...+38+39+40 ??

Arithmetic progression = 20[2+39]
= 20*41
= 820

Hence tens digit =2

Heman
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Joined: 21 Jun 2006
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Kudos [?]: 34 [0], given: 0

for n consecutive integers,
sum is n(n+1)/2
for 40 integers consecutive - 40*41/2=820

Tens digit 2
Intern
Joined: 08 May 2006
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the ten digit is 2.

Sum of first n number is n( n+1) /2 = 40 ( 41) /2 = 820

tenth Digit is 2
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