Consider 1.3567 which has 4d.p. and 5s.f. plus 0.6 which has 1d.p and 1s.f. When you add the two together you get 1.9567 but you must leave answer to one dp so it should be 2.0 which has 1dp and 2sf.
If you were to multiply the two numbers together u get 0.81402 which will be 0.8 because it...