$\frac{50.0-25.0}{62.5-25.0}=\frac{25.0}{37.5}=0.666$	$\frac{50.0-37.5}{75.0-37.5}=\frac{12.0}{37.5}=0.333$
Dose log dose	$\frac{21.5}{8.6}=2.5$
21.5 1.3324	log 2.5 = 0.3979
8.6 0.9344	0.333 × 0.3979
=0.398	0.1325007
∴ 0.666 × 0.3989 = 0.265068
Antilog of 0.9344 + 0.265068	Antilog of 0.9344 × 0.1325007
=1.199468	=0.12380
MLD50 = 15.82 mg/mouse	=1.32
	MSD50 = 1.33 mg/mouse
$\text{Therefore,}\text{IMLD}=\frac{{\mathit{MLD}}_{50}+{\mathit{MSD}}_{50}}{2}=\frac{15.82+1.33}{2}=\frac{17.15}{2}$
=8.75 mg/mouse