number series

Look at this series: 31, 29, 24, 22, 17, ... What number should come next?

Look at this series: 1.5, 2.3, 3.1, 3.9, ... What number should come next?

Look at this series: 14, 28, 20, 40, 32, 64, ... What number should come next?

Look at this series: 2, 4, 6, 8, 10, ... What number should come next?

Look at this series: 201, 202, 204, 207, ... What number should come next?

Look at this series: 544, 509, 474, 439, ... What number should come next?

Look at this series: 80, 10, 70, 15, 60, ... What number should come next?

Look at this series: 2, 6, 18, 54, ... What number should come next?

Look at this series: 5.2, 4.8, 4.4, 4, ... What number should come next?

Look at this series: 8, 6, 9, 23, 87 , ... What number should come next?