Is it possible to count some numbers in a range(Descending order range)

Is it possible to count some numbers in a range(Descending order range), where those some numbers forms round about 50% of the total sum of the range.

ex-
A 2742819 20.30%
B 1781170 13.18%
C 1555761 11.51%
D 1504020 11.13%
E 1037787 7.68%
F 943238 6.98%
G 929913 6.88%
H 890030 6.59%
I 738115 5.46%
J 707029 5.23%
K 682963 5.05%
SUMTOTAL 13512844 100.00%

Here the range is in descending order.
Now here I want to count the number of items summing to 50% of the total value(i.e 50% of 13512844).
I have to manually sum to round about of 50%(+/- 2%) and count the individual values that how many have come under that 50%.

is there any formula for that? because I have to do same work for 500 times.