How do you do this?!
Evaluate 1+3+5+7......+101

Is the answer 5202? I don't think so though......
my method was
101+1=102
102/2=52
52x102=5202

Maple Tan wrote:
How do you do this?!
Evaluate 1+3+5+7......+101

Is the answer 5202? I don't think so though......
my method was
101+1=102
102/2=52
52x102=5202

Err, from 1-101, there are 51 odd numbers.

There are 50 odd numbers from 1-100

99+1=100
100x50=5000
5000+101=5101

Oops I went to calculate the sum of ALL numbers from 1-101.

Sorry both answers are incorrect.

There is a fast way using a formula or a derived way. I will derive the solution.

First find the sum of all of the integers up to 101.
1+2+3+ ...+ 99+100+101
--> 101x102 / 2
--> 5151

Now find the sum of all the even numbers from 2 to 100
2+4+6+ ... +98 + 100
--> 2 x (1+2+3+ ... + 50)
--> 2 x (50x51 / 2)
--> 2550

Subtracting
5151 less 2550 --> 2601

The fast formula way is
(n+1) / 2 = ans
ans x ans


Eg. using this question the last number is 101. So
102/2 = 51
51 x 51 = 2601