In reply to The Ice Doctor:
For a "back of a fag packet" calculation for non mathematicians....
Round 2.9 trillion up to 3 trillion to make the figures easier.
Using currently used definitions of billion/trillion you now have .....
(60 thousand million) divided by (3 thousand thousand million)
The 'thousand million bits cancel out so it's the same as ......
60 / 3000
Take a zero off both....
6/300
Divide both by 3....
2/100 = 2%
Remembering that you rounded up the larger figure, the actual result will be a little bit higher than this.