Intermediate species	Number of Hybrid orbitals
Carbocation	A
Carbanion	B
Free Radical	C
Singlet Carbene	D
Triplet Nitrene	E

Then, the value of  $\frac{A+B+C-D-E}{3}$

carbocations undergoes $s{p}^2$ hybridization, hence 3 hybridorbitals 
Carbocations undergoes $s{p}^2$  hybridization, hence 4 hybridorbitals
Free radicals $s{p}^2$ hybridization, hence 3 hybridorbitals
Singlet carbenes $s{p}^2$  hybridization, hence 3 hybridorbitals
Triplet Nitrenes  $sp$ hybridization, hence 2 hybridorbitals
Hence $\frac{A+B+C-D-E}{3}$ is 1.66