Math problem

Big J: How many miles is 623 km?

Me: About 400.

Dad: Let me figure it out... you need to divide by 1.61 ::gets out pen and paper::

Big J: Never mind, I'll find a calculator.

Dad: 387 or so.

Mom: Misstea said "about 400!"

Big J: :: playing with the calculator on his phone:: So I got 18 miles to the gallon. Good to know.

Me: Is that kettle going to be boiling any time soon?