145. Solving a chemistry problem

71. When determining lead in an alloy, the calibration graph method was used, which was built according to the following data:
Conc. standard solution of lead μg / ml 2.0 4.0 6.0 8.0 10.0
Atomic absorption at 283.3 nm 0.160 0.320 0.480 0.640 0.800
A portion of the alloy weighing 0.5000 g was dissolved in a mixture of acids and transferred to a volumetric flask with a capacity of 250.00 ml. Before analysis, the solution was diluted 20 times. The atomic absorption of this solution is 0.500. Determine the mass fraction of lead in the alloy.