11.7 Proficiency exam

( [link] ) Solve using graphing: $\{\begin{array}{c}3x+2y=4\\ 15x+10y=-10\end{array}$

( [link] ) Solve using graphing: $\{\begin{array}{c}2x-3y=2\\ x+2y=8\end{array}$

( [link] ) Solve using substitution: $\{\begin{array}{c}2x+6y=16\\ x-4y=-13\end{array}$

( [link] ) Solve using addition: $\{\begin{array}{c}3x+8y=-5\\ x-2y=3\end{array}$

( [link] , [link] ) Solve using either substitution or addition: $\{\begin{array}{c}4x-4y=8\\ x-y=5\end{array}$

( [link] , [link] ) Solve using either substitution or addition: $\{\begin{array}{c}9x+3y=12\\ 3x-y=4\end{array}$

( [link] ) The sum of two numbers is 43 and the difference of the same two numbers is 7. What are the numbers?

( [link] ) A chemist needs 80 ml of an 18% acid solution. She has two acid solutions, A and B, to mix together to form the 80-ml solution. Acid solution A is 15% acid and acid solution B is 20% acid. How much of each solution should be used?

( [link] ) A parking meter contains 32 coins. If the meter contains only nickels and quarters, and the total value of the coins is $\$4.60$ , how many of each type of coin are there?

( [link] ) A person has $15,000 to invest. If he invests part at 8% and the rest at 12%, how much should he invest at each rate to produce the same return as if he had invested it all at 9%?