Step 1 :Let Pleasanton's initial population in 1980 be \(x\).
Step 2 :Population decreased by \(10\%\) in 1980s: \(0.9x\).
Step 3 :Population increased by \(20\%\) in 1990s: \((1+0.2)(0.9x) = 1.08x\).
Step 4 :Percentage increase at end of 1990s: \(\frac{1.08x - x}{x}\times 100 = 8\%\).