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Last Word is Â鶹´«Ã½â€™s long-running series in which readers give scientific answers to each other’s questions, ranging from the minutiae of everyday life to absurd astronomical hypotheticals. To answer a question or ask a new one, email lastword@newscientist.com

How much money is gained or lost in computer rounding errors in, say, a year? And what happens to this money?

Adrian Bowyer,

Foxham, Wiltshire, UK

There are millions of tonnes of white hydrogen available for power. Since each reaction needs oxygen, could it deplete our air supply?

Colin Horwood,

Salthouse, Norfolk, UK

To answer this question –…