Mike has 21 books and 44 magazines in his library. He bought several books at a yard sale over the weekend. He now has 77 books in his library. How many books did he buy at the yard sale ?

Add the fractions and simplify 1/2+ 1/3

Which shows the correct substitution of the values a,b and c from the equation 1=-2x+3x^2+1

Se tiene en una caja de canicas 10, 4 blancas y 6 negras ¿cual es la probabilidad que en 2 extracciones con reemplazo sean blancas? ¿cual es la probalidad que en 2 extracciones sin reemplazo sean negras?