The postal service charges $.49 for letters that weigh 1 ounce or less and 21 cents more for letters that weigh between 1 and 2 ounces. Alivia, testing her dad's math skills, gave her dad $49.70 and asked him to purchane 80 stamps for her stamp collection, some 49 cents stamps and some 70 cent stamps. How many of each type of stamp did her dad buy if he used all the money

What is the main difference between primary and secondary sources? a. primary sources are historical documents, and secondary sources are modern-day documents. b. primary sources are derived from museums and archives, and secondary sources are created by history students and academics. c. primary sources are found in ancient places with a rich history, and secondary sources are found in historical journals and blogs. d. primary sources are created during a particular historical era, and secondary sources are created by studying primary sources.