In each blank below a single digit is inserted such that the following six three-digit numbers in this order, form an arithmetic sequence:
125, 129, 1_ _, 1_ _, 1_ _, 1_ _
What are the missing digit?
What is the difference between the first and the second term?
129 - 125 = 4 - is the common difference. Then just add 4 to each term.
125, 129, 133, 137, 141, 145......etc.
