Answer: Problem 4, missing number is 626, while the missing number for all the other problems is 426.
Step-by-step explanation:
Problem 1. 526= _ + 100 (Ans = 526-100=426)
Problem 2. 526-_=100 (Ans = 526-100=426)
Problem 3. 526-100=_ (Ans = 526-100=426)
Problem 4. 526+100=_ (Ans = 526+100=626)