Asked by chelly
                it takes 6 cubes to build a staircase with 3 steps. how many cubes will be needed for 11 steps?
            
            
        Answers
                    Answered by
            Reiny
            
    1 step -- 1 cube
2 steps - 3 cubes
3 steps - 6 cubes
4 steps - 10 cubes
.....
n steps - n(n+1)/2 cubes
so 11 steps --11(12)/2 = 66 cubes
these are called the triangular numbers
think of it as the sum of billiard balls when they are racked up
1st row -- one ball
2 rows --- 3 balls
etc.
    
2 steps - 3 cubes
3 steps - 6 cubes
4 steps - 10 cubes
.....
n steps - n(n+1)/2 cubes
so 11 steps --11(12)/2 = 66 cubes
these are called the triangular numbers
think of it as the sum of billiard balls when they are racked up
1st row -- one ball
2 rows --- 3 balls
etc.
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