You can look at it this way: the electricity bill will be divided equally among four people in the first 10 days.

Five people will share it equally for the next 20 days.

905.7× 1/3÷4+905.7×2/3÷5

=75.475+ 120.76

= 196.235

But it is not the most standard, because the electricity consumption in the first 10 day should be less than that in the whole month 1/3. If the electricity consumption before 10 is not recorded, it is only an estimate. Strictly speaking, four people are less than 196, and the fifth person should be extra 120. The second one is relatively reasonable.