This is just a misunderstanding, and the calculation method itself has problems, so there is no doubt that there is 10 yuan.
This is obviously deliberately confusing the topic! Mislead with the wrong description! The following is a detailed explanation!
Total amount 1000=A (owed to mother 490)+B (owed to father 490)+C (paid to mother 10)+D (paid to father 10)= E (paid to shoes 970)+F (remaining 30).
G (money left in pocket) = total amount 1000-E-C-D= 10 yuan.
F=C+D+G
A+B+G=990 (that's why it's 990) (know that 10 in your pocket is included in the money you borrowed).
A+B+C+D= 1000 (this is correct).
A+B=E+G