self Maths Puzzle

6.25:1.5811::??:1.8708

Find it? With explanation.

Read Solution (Total 2)

self Other Question

Find first and last value in the below series

???, 0.57735, 0.44721, 0.37796, ???
In the word RAINBOW how many words are there in which A is always before I and I is always before O?
a)840
b)420
c)720
d)none of these

please explain the method clearly