Determining the gravity of 2 mixed worts - how?

[spearmint-wino]

Hi all

In trying to work out a pre-boil gravity I've got a boiler with 27.5l of 1.047 and a further 4l of 10.14 to top up with - how do I work out the gravity of these worts when mixed together?

I'm sure it should be easy, but as I may have said before, my maths ain't good...

thx.

EDIT: I mean determining the gravity before you mixed them, finding out once you've mixed them I think I have a grasp of

[anomalous_result]

The total volume is 31.5 so do this:

1.047 * (27.5/31.5) + 1.014 * (4/31.5) = 1.043

I reckon.

[spearmint-wino]

Sounds about right. Thanks!