Strictly speaking 1:50 and 1+50 mean the same to me and to most chemists and technical people. Same goes for 1:49 and 1+49..

1:50 gives 51 parts and 1:49 gives 50 parts. It is normal to mix up to a given total such as 50 parts or 10 parts.

So, a 10% solution is 1:9 or 10 ml of A and 90 ml of B.

PE