Can you tell hoe long I have to roast my leg of lamb for please

[Usthree]

It weighs 1.115 kg. The instructions say roast for 25 mins per 500g plus 25 mins.

How long is that?

obviosuly, "the rest of the time" is based roughly on the calculation we've done earlier on here so for 1.8kg it would be about 100 odd minutes give/take in total.