first, add up the parts of the ratio...
2+3+5=10
then divide the whole into individual parts...
25/10=2.5
then multiply the value of 1 part by the amount in the ratio...
2.5 x 2 =5
2.5 x 3 = 7.5
2.5 x 5 = 12.5
so the final ratio is 5kg:7.5kg:12.5kg
Hope this helps :)