My six-year-old daughter enjoys addition but not subtraction. When we walk together, I like to give her some "mental mathematics" questions, such as "What is 13 plus 33" and she enjoys answering them. However, she always asks me to give her addition problems only. So she will refuse to answer the question "What is 21 minus 6".
I have discovered a "trick" that works for her: I will ask the question "What is 21 plus negative 6" and she will give me the answer 15. But still, she will not do 21 minus 6.
Is it normal for her to dislike subtraction while enjoying addition? Is there anything that I can/should do about it other than converting a subtraction problem to an addition problem?