The flower bed has:
- Row 1: 23 plants
- Row 2: 21 plants
- Row 3: 19 plants
- Last row: 5 plants
Each row has 2 fewer plants than the previous row (23 → 21 → 19).
This is an arithmetic progression with common difference d=−2.
For an arithmetic progression, the nth term formula is:
an=a+(n−1)×d
Where:
- an=5 (plants in last row)
- a=23 (plants in first row)
- d=−2 (common difference)
- n=? (number of rows)
Substituting the values:
5=23+(n−1)×(−2)
5=23−2(n−1)
5=23−2n+2
5=25−2n
2n=25−5
2n=20
n=10
Therefore, the number of rows in the flower bed is 10.