A peak stands at a height of 1200 metres and a valley floor lies at a height of -150 metres. What is the difference in height, in metres?

Explication

The valley floor lies one hundred and fifty metres beneath sea level and the peak twelve hundred metres above it, so a climb from one to the other covers both of those distances added together. Taking one hundred and fifty away from twelve hundred would be right only if the valley floor stood above sea level as well.