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A brick staircase has a total of 17 steps, with the first step requiring 118 bricks. Each successive step requires 5 less bricks than the prior one. How many bricks are required to build the staircase?

 Apr 11, 2020
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To find the total number of bricks, you can use this formula:  Sum  =  n(t1 + tn) / 2

where  n = number of numbers = 17

           t1 = first number = 118

           tn = last number =  ??

 

To find tn, you can use the formula:  t= t1 + (n - 1)·d

where d = common difference = -5

--->   tn  =  118 + (17 - 1)·(-5)  =  38

 

--->   Sum  =  17(118 + 38)/2  =  1326 bricks.

 Apr 12, 2020

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