Question

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

last year. ​

Answer 1

80

Explanation:

new value = 84

old value = n

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

`(84-n)/(n)` =
`(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

Answer 2

80%

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!