Answer :
When dealing with weighted averages, we multiply the score of each item by the percentage that it's been weighted and add the scores together.
80/100 X 70/100 = 5600/10000 or 56/100
50/100 x 30/100 = 1500/10000 or 15/100
56 + 15 = 71 and so your grade would be 71%