Respuesta :

763396

Answer:

80%

Step-by-step explanation:

Let's call the past exam mark m,

m*105%=84

m*105/100=84

m=84/(105/100)

m=80

Hope this helps!

clarch19

Answer:

80

Step-by-step explanation:

new value = 84

old value = n

can use percent change formula:  (new value - old value) / old value = 5/100

[tex]\frac{84-n}{n}[/tex] = [tex]\frac{5}{100}[/tex]

cross-multiply (you can simplify 5/100 to be 1/20 first):  20(84 - n) = n

1680 - 20n = n

1680 = 21n

n = 80