The teacher will be very surprised to see your correct solution 😉
/ x \ 1 + erf|-----| | ___| \\/ 2 / 39 -------------- = -- 2 40
___ /19\ x1 = \/ 2 *erfinv|--| \20/
x1 = sqrt(2)*erfinv(19/20)
sum
___ /19\ \/ 2 *erfinv|--| \20/
=
___ /19\ \/ 2 *erfinv|--| \20/
product
___ /19\ \/ 2 *erfinv|--| \20/
=
___ /19\ \/ 2 *erfinv|--| \20/
sqrt(2)*erfinv(19/20)