A string of numbers are arranged according to the following rules: 5, 7, 9, 1 1, …, 47, 49. Excuse me:
(1) What is the number 16 in this column?
(2) Where is this column 43?
Analysis: By observing this series, it is found that the first term is arithmetic progression with a tolerance of 2, which can be solved according to arithmetic progression's general term formula.
Solution: Solution: (1) 5+(16-1) × 2.
=5+30
=35
A: The number 16 in this column is 35.
(2)(43-5)÷2+ 1
=38÷2+ 1
=20
Answer: 43 is the 20th in this column.
Comments: arithmetic progression's general formula an=a 1+(n- 1)d is mainly used to solve the problem flexibly.