How does 31,000 equal 50,000?

It does if you believe everything you read in political manifestos.
I don’t generally believe everything I read in the Daily Mail, indeed I don’t read the Daily Mail because of its blatant political bias. I was therefore so surprised that they published this article (and gave link to video) that showed the Health Secretary being lambasted for trying to convince the viewers that 31,000 nurses was the equivalent to 50,000 more nurses. See:

https://www.dailymail.co.uk/news/article-7722981/Piers-Morgan-tears-Nicky-Morgan-GMB-nonsense-pledge-50-000-NHS-nurses.html

I’m sure she would have put forward similar arguments for the “increase” in police numbers.

Just the pity that so many will believe these promises just like the Brexit bus and it’s pronouncement on the windfall the NHS would get if we voted to leave the EU.
No wonder an increasing number of voters think that politicians are not trustworthy.