I also fail in calculation. But,

- how long to boil water in kettle on gas stove? 23 minutes on blue flame, not yellow flame.

- how long it takes on electric kettle?

- how many kettles can u boil on a single gas tank? Divide.

- How many kwh used for the same amount of kettles used to boil with electric? Divide.

- Take gas price per kettle, take electric price per kettle.

Aiyaaaaa dunno la.

I boil water with gas and electric. Yes electric is slightly faster but i do not know of the cost of neither. Most homes have these electric water boiler with keep hot function. Those suck electric like mad as u use it 24 hours a day. I boil with electric water pot and then transfer the water to a thermos. The water boiled by gas is cooled for regular consumption. I use my handphone alarm function to keep track when the water boils. It averages 23 minutes depending on weather.