Answer :
R = 6.25%
Solution,
Let P is the principal. It means interest will be :
I=3/8 P
The formula for the interest is given by :
[tex]I=\dfrac{PRT}{100}\\\\\dfrac{3}{8}P=\dfrac{PR\times 6}{100}\\\\\dfrac{3}{8}=\dfrac{6R}{100}\\\\R=\dfrac{300}{8\times 6}\\\\=6.25\%[/tex]
Hence, the rate of interest is 6.25%.