A bag contains purple marbles and blue marbles, 29 in total. The number of purple marbles is 1 less than 2 times the number of blue marbles. How many purple marbles are there?
+538 Lets say the number of blue marbles in the bag is X. That would make the number of purple marbles 2X-1. Combined, that makes 3X-1.
Now 3X-1=29. If we add 1 to each side we get 3X=30. Divide both sides to get X=10. Now we said that the number of purple marbles is 2X-1. Substitue in 10 to get that there are
19 purple marbles in the bag.
