The sum of each problem is 100. You need to find the missing number. Look at the given number and raise it up to the next multiple of 10 and then "count up" by tens to 100. You may want to use a "Hundreds Chart" to help you 'see' the problem and answer.
45 + _ = 100 45 needs 5 to reach 50, then count up, 60, 70, 80, 90, 100, so 5 and 5 tens, or 55.
_ + 65 = 100 65 needs 5 to reach 70, then count up, 80, 90, 100, so 5 and 3 tens, or 35.
Follow this method to find the missing number. Strive for accuracy and then strive to increase your speed. Good luck and enjoy the challenge!