Logical Reasoning

Sequence & Series

Medium

In a row of students, there are 27 students in first row, 24 in the second, 21 in the third, and so on. There are 6 students in last row. How many students are there in all row?

120

123

132

135

✅ Correct Option: 3

The numbers form an AP with first term $a = 27$ and common difference $d = -3$ .

Using $a_n = a + (n-1)d$ : $6 = 27 - 3(n-1)$ , so $n - 1 = 7$ and $n = 8$ rows.

Sum $= \frac{n}{2}(a + l) = \frac{8}{2}(27 + 6) = 4 \times 33 = 132$ .

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2023: 7 June Shift 1

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Solution