The first step of a staircase is 30 cm wide

MATHEMATICS · Single correct · CBSE · Mathematics · Arithmetic Progressions · Arithmetic Progressions

Problem

The first step of a staircase is 30 cm wide, and the width of the steps decreases uniformly so that the 10th step is 21 cm wide. Which one of the following is the common difference (in cm) of the arithmetic progression formed by the widths of the steps? (a) −9 cm-9\,\text{cm} (b) 1 cm1\,\text{cm} (c) −1 cm-1\,\text{cm} (d) −0.9 cm-0.9\,\text{cm}

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