5.8 x 2.19
= (5.00 + 0.80) x (2.00 + 0.19)
= 5.00*2.00 + 5.00*0.19 + 0.80*2.00 + 0.80*0.19
= 10.00 + 0.95 + 1.60 + 8/10 * 19/100
= 10.00 + 0.95 + 1.60 + (8*(10+9))/1000
= 10.00 + 0.95 + 1.60 + (80+72)/1000
= 10.00 + 0.95 + 1.60 + 152/1000
= 10.000 + 0.950 + 1.600 + 0.152
= 11.600 + 0.950 + 0.152
= 12.550 + 0.152
= 12.702
It actually is a reasonable value.