Question

A stack of squares has 170 squares in the bottom row, 156 in the second row from the bottom, 142 in the third row from the bottom and 128 in the fourth row from the bottom. How many squares will there be in the 11th row from the bottom ? - a table always makes these sums easier!)​

Answer 1

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Answer:

  30

Step-by-step explanation:

The sequence of square counts is ...

  170, 156, 142, 128

The differences from one row to the next are ...

  -14, -14, -14

We see that the differences are constant, so we know the sequence is an arithmetic sequence with first term 170 and common difference -14. This means the n-th term is ...

  an = a1 +d(n -1) . . . . . . for first term a1 and common difference d

  an = 170 -14(n -1)

For n=11, the number of squares is ...

  a11 = 170 -14(11 -1) = 30

There will be 30 squares in the 11th row.