6(1)In any case where;—
(a)part only of a holding of qualifying investments is treated for the purposes of estate duty as passing on a death, and
(b)investments comprised in that holding are sold as mentioned in paragraph (c) of subsection (1) of the principal section,
the principal section and this Schedule shall apply as if the entirety of the holding fell within paragraph (a) of subsection (1) of that section and, if a claim is made under that section in respect of the investments referred to in paragraph (b) above, the dutiable fraction of the principal value of the investments to which the claim relates, as determined under that section, shall be the principal value of that part of those investments which is treated as passing on the death.
(2)In sub-paragraph (1) above, " dutiable fraction " means the fraction of which the numerator is the basic principal value of the part of the holding referred to in paragraph (a) of that sub-paragraph and the denominator is the basic principal value of the entirety of that holding.