During a sale , customer spent exactly $260 on sweaters , jeans and shoes . Each sweater cost $25, each pair of jeans costs $50, and each pair of shoes cost $20. The customer bought twice as many sweaters as pair of shoes . The customer purchased 10 items. Let x= the number of sweaters, y=the number of pairs of jeans and z= the number of pairs of shoes you should buy. Write the systems of equations .

Researchers are conducting experiments to determine the role of alcohol in the development of depression. after the study is complete, they determine that the relative risk of developing depression is 1.55 with a 95 % ci of 1.2 -1.9. each group is then divided into nonsmokers and smokers. the relative risk for the nonsmokers is 1.12 with a 95% ci of 0.87-1.37. the relative risk for the smokers is 1.7 with a 95 % cl of 1.5-1.9. what type of bias may affect this study? a. procedure bias b. recall bias c. selection bias d. confounding e. lead-time bias