Processing math: 100%
 
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avatar+766 

Evaluate 21 + 27 + 33 + ... + 267 + ... + 6021.

 Mar 2, 2025
 #1
avatar+35 
+1

Please think this problem through, it is a basic problem that shouldn't require any help. Here are some hints: 

 

Note that each number is 6 plus the last number. So can we manipulate the sum to be divisible by six? That way we can apply the formula 1+2+...+n=n(n1)2

 Mar 2, 2025
 #2
avatar+130458 
+1

Sum =  [first term + last term ] * [number of terms / 2]

 

Nuimber of terms =   [6021 - 21 ]  / 6   +  1    =  1001

 

Sum =   [ 21 + 6021 ] *  [ 1001 / 2 ] =   3,024,021

 

cool cool cool

 Mar 3, 2025

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