Number25 it says thirty cubes were used to construct this 3 step staircase how many cubes would be used to construct a 10 step staircase of the same width

This can be represented by the sequence  5 , 10 , 15
- Arithmetic sequence with common difference 5

The sum of  n terms = (n/2) [2a1 + (n - 1)d]

S10  = (10/2)[2*5 + (10-1)*5]
         = 5 * (10 + 45) 
         = 5 * 55
         =  275 
So the answer is 275 cubes

The answer to your question is 275 cubes

I'm sure the answer is a

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