Years Purchase, dual rate              
with income tax            
(quarterly in advance)            
1            
4[1 - (1+r)-1/4] +  4[1-(1+a)-1/4] * TG      
  (1+a)n -1      
Amount (£)      
Interest Rate (%)          
Term (years) (n)      
Sinking Fund (%)          
Tax Rate (%)          
       
Answer (£)      
1
(1+r) (1+a)
4[1 - (1+r)-1/4] +  4[1-(1+a)-1/4]
(1+r)^-1/4 (1+a)^n
(1+a)n -1
1-(1+r)^-1/4 (1+a)^n-1
b 4[1 - (1+r)^-1/4 
Effective yield [r] (1+i/p)^p -1
(1+a)
p = no of times int
(1+a)-1/4
is received and
[1 - (1+a)-1/4 ] 4[1-(1+a)-1/4]
compounded 
4[1-(1+a)-1/4] (1+a)n-1
during the year
Tax
1 TG
1-x x Rate of Tax
100