In a flower bed, there are 23 rose plant in first row, 21 in 2nd row, 19 in…
2022
In a flower bed, there are 23 rose plant in first row, 21 in 2nd row, 19 in 3rd row and so on. There are 5 rose plants in last row. How many rows are there in the flower bed?
- A.
8
- B.
9
- C.
10
- D.
11
Attempted by 48 students.
Show answer & explanation
Correct answer: C
Solution: Find the number of rows by treating the counts as an arithmetic sequence.
This is an arithmetic sequence with first term 23, last term 5, and common difference −2.
First term (a1) = 23
Last term (an) = 5
Common difference (d) = −2
Formula: n = ((last − first)/common difference) + 1
Compute n: n = ((5 − 23)/(−2)) + 1 = (−18/−2) + 1 = 9 + 1 = 10
Answer: 10 rows.
Sequence check: 23, 21, 19, 17, 15, 13, 11, 9, 7, 5 (10 terms)