Solve this system of equations algebraically:
y + x = 19 – x2
x + y = 80
1. isolate one variable in the system of equations. y = –x2 – x + 19
y = –x + 80
2. use substitution to create a one-variable equation. –x + 80 = –x2 – x + 19
3. solve to determine the unknown variable in the equation.

the system has
real number solution(s).

In a singing competition, there are 150 participants. at the end of each round, 40% of the participants are eliminated. how many participants are left after n rounds?

Ana earns 2.5% simple interest on $2,000 in her savings account. she does not make any deposits or withdrawals. after 3 years, how much interest will ana have earned on her savings account?

Which of the following would be a correct step in proving that triangle abc is congruent to triangle cda? a. use a protractor to measure the angles and show that all the corresponding angles are equal in measure. this will allow you to prove congruence by aaa. b. show that segment ab is parallel to segment cd and segment ad is parallel to segment cb. this will allow you to prove congruency by asa. c. show that is segment ab is perpendicular to segment ad. this will allow you to prove congruence by sas. d. none of the above.