## Stony Brook University MAT 118 Spring 2013

### Assignment 9 due in Recitation, week of April 8

A. Prime numbers
1. Mindscape 8 page 81
2. Mindscape 11 page 81
3. Mindscape 14 page 81. (The Goldbach Conjecture is stated on page 80).
4. Mindscapes 23, 24, 25 page 82.
B. Clock arithmetic and check digits
1. Find two barcodes and study the UPC numbers. Check that the sum $3d_1+d_2+3d_3+d_4+3d_5+d_6+3d_7+d_8+3d_9+d_{10}+3d_{11}+d_{12}$ is always a multiple of $10$ ("equivalent to $0$ mod $10$"). Explain carefully why any missing number can be restored if the other eleven are known. Show for one of your barcodes how $d_2$ can be retrieved if it is missing. Same for $d_3$.
2. Mindscapes 1, 2, 3, 4 page 92. "Reduce $7$ mod $3$" means give the remainder when $7$ is divided by $3$. Equivalence is discussed on page 88.
3. Mindscapes 27, 28, 29 page 95.

Remember: Collaboration is fine, but what you hand in should be your own work. Handing in something you copied is plagiarism and will cost you if it is detected. Write down what you tried and how it worked.