[sn41]

I suppose you have heard about the rule of 72 - it's quite useful for roughly figuring out doubling rate from compound interests, and vice versa:

https://en.wikipedia.org/wiki/Rule_of_72

I guess doubling in 10 years corresponds to annual percentage of 7.2 percent, and 20 years, 3.6 percent. Adjusting for inflation, the rate will be lower.

BTW, you may be referring to Unit-linked insurance schemes. They are neither good as insurance, nor good as investments.