1. Element A has two isotopes. The first isotope is present 34.01% of the time and has a mass of 137.11. The second isotope has a mass of 111.37. Calculate the atomic mass of element A. (To two decimals places)

2. Element A has two isotopes. The first isotope is present 6.95% of the time and has a mass of 259.87. The second isotope has a mass of 200.17. Calculate the atomic mass of element A. (To two decimals places)

3. Element R has three isotopes. The isotopes are present in 0.0398, 0.1614, and 0.7988 relative abundance. If their masses are 198, 176, and 145 respectively, calculate the atomic mass of element R. (No decimals)

4. Element R has three isotopes. The isotopes are present in 0.0825, 0.2671, and 0.6504 relative abundance. If their masses are 89, 113, and 131 respectively, calculate the atomic mass of element R. (No decimals).