Question

A 70% decrease of 270

Answer 1

A 70% decrease means you are left with 30%.
0.3*270 = 81

Alternatively, there is the formula New number = (1-r)*number
New number = (1-0.7)*270
New number = 0.3*270
New number = 81

Answer 2

A 70% decrease of 270 would then be 189