Question

John's Mathematics exam mark this year is increased by 5% to 84. Find his Mathematics exam mark
last year. ​

Answer 1

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!

Answer 2

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

$\frac{84-n}{n}$ = $\frac{5}{100}$

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

1680 - 20n = n

1680 = 21n

n = 80