Final answer:
Mary sold 5 necklaces and 15 bracelets.
Step-by-step explanation:
To find the number of necklaces and bracelets sold by Mary, we can set up a system of equations based on the given information. Let's let 'x' represent the number of necklaces and 'y' represent the number of bracelets. We know that Mary sold a total of 20 necklaces and bracelets, so we can write the equation: x + y = 20. We also know that she sold 3 times as many bracelets as necklaces, so we can write the equation: y = 3x. Solving this system of equations, we can substitute the second equation into the first equation to get: x + 3x = 20. Combining like terms, we have 4x = 20. Dividing both sides by 4, we find that x = 5. Plugging this value back into the second equation, we can find y: y = 3(5) = 15. Therefore, Mary sold 5 necklaces and 15 bracelets.