Is 74% my overall mark in English?

Question

my English exam is worth 15% of my final mark, Before writing the exam, my overall mark was a 78. and I passed the English exam by getting a 50% on it.

and someone calculated my overall mark for me by doing this:

78 X .85 = 66.3

50 X .15 = 7.5

66.3 + 7.5 = 73.8, which rounds to 74.

i'm just wondering, why would this person multiply 78 X by .85?

what's the .85?

Answer 1

The 78 is your grade before the exam and is 85 percent of your grade which therefore makes it acceptable to multiply it by .85 and then multiply the exam grade by the percentage that it is worth, hence the .15 and then add those two numbers which yes does make your grade a 74%

Answer 2

they multiplied it by .85 because if your exam was worth 15% that means the rest was worth 85% aka .85.

Answer 3

because, if the exam is 15%, everything else is 85% or .85. Since your grade was a 78, 85% of that is 66.3.