When adding 10 to any two digit number, increase the left digit by 1. For example 20+10= 30. 55+10=65. If a problem says 10+ (a number), you can reverse the order the numbers are in because of the commutative property of addition. Example: 10+50 eqauls 50+10. Both equations equal 60. Also, Rodney would have 39 pieces of fruit since 20+19 is 39.