Human: Lizzy's school choir has a mixture of 80 blonde and black-haired girls. Their teacher decides to add 10 more girls to the choir, who turns out to be blonde. If there were 30 blonde-haired girls in the choir initially, how many black-haired girls are present? Assistant:
The total number of girls in the choir is 80+ 10 = 90 girls.
The total number of blondes in the choir after 10 more are added is 30+10 = 40 blonde-haired girls.
From the total number, the number of black-haired girls is 90-40 = 50 black-haired-girls