When you need to add 2 numbers and one number is 1 greater than the other, you are "adding doubles plus 1". The sum is simply the smaller number, doubled plus 1. The answer is always an odd number.
15 + 16 Convert to: 15 + 15 + 1 = 30 + 1 = 31 Easy!
11 + 12 Convert to: 11 + 11 + 1 = 22 + 1 = 23 Easy!
Use this technique to find the answer for these 'adding doubles plus 1' problems. Strive for accuracy and then strive to increase your speed. Good luck and enjoy the challenge!