70 pennies decreased by 20% is
56 pennies.That is, \(70*\frac{100-20}{100}=70*\frac{80}{100}=70*\frac{4}{5}=\frac{4*70}{5}=4*14=56\)
56 pennies, you should find 20% of 70 to get 14 and subtract that from 70 to get you answer.