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What is 75 + 72 + 69 + 66 + ... + 21 + 18 + 15 + 12 + 9 + 6 + 3?

 Jul 27, 2022
 #1
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Expain how to calculate 75 + 72 + 69 + 66 + ... + 21 + 18 + 15 + 12 + 9 + 6 + 3

 Jul 27, 2022
 #2
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We have      (75 - 3)   / 3  +   1 =    72/3  + 1 =  24 + 1  =    25  terms

 

Sum  =  

 

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

 

[ 75 + 3 ]  *  ( 25 / 2)  =

 

 ( [ 78 ]   / 2 )  *  25   = 

 

39 * 25   =

 

975

 

cool cool cool

 Jul 27, 2022

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