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?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 132
The numbers 27, 24, 21, … 6 form an arithmetic progression with first term 27 and common difference −3. From 6 = 27 − 3(n − 1) we get n = 8 rows.
The total is the sum of the progression, (n/2)(first + last) = (8/2)(27 + 6) = 4 × 33 = 132 students.