doubt 19

[aditya8062]

Although the initial setup of generators and a power grid by Edison and JP Morgan
was rather costly, the electrification of lighting in lower Manhattan doubled work
efficiency when the energy costs were cut in half.

(A) the electrification of lighting in lower Manhattan doubled work efficiency
when the energy costs were cut in half
(B) the electrification of lighting in lower Manhattan doubled work efficiency
while cutting energy costs in half
(C) the electrification of lighting in lower Manhattan doubled work efficiency
while costs were cut to half
(D) lighting electrification in lower Manhattan doubled work efficiency while energy
costs were cut in half
(E) lighting electrification in lower Manhattan doubled work efficiency while
costs were cut to half

my doubt: i cannot understand as why the expression "while cutting energy costs in half" is correct? can energy costs be cut in half? i feel that energy costs can be cut to half

[GMATGuruNY]

my doubt: i cannot understand as why the expression "while cutting energy costs in half" is correct? can energy costs be cut in half? i feel that energy costs can be cut to half

One definition of to cut X in half is to reduce X by 50%.
Thus, it is idiomatically correct to say while cutting energy costs in half.
Conveyed meaning:
while reducing energy costs by 50%.