Question 1040424
x=3%; (1/2)x=5%, 50000-(3/2)x=4.5%.  Twice as much is in the lower as the upper, not the reverse
.03x+0.045(50000-(3/2)x)+0.05(1/2)x=1900
.03x+2250-.0675x+0.025x=1900
-0.0125x=-350
x=28000@3%=840
z=14000@5%=700
the 4.5% is 8000=360
They add to 1900.
It can be done with x+y+z=50000
.03x+.045y+.05z=1900
but the way you used if you make y=50000-x-(1/2)x) is easier