"Way1: THere are 10x20ml in 200ml so moles of Pb(NO3)2 is 0.3598445."
In your case, you have 0.36 mol/200mL but you want mol/L, so times further by 5 i.e. (0.36 x 5)/(200mL x 5) = 1.80 mol/L
Though, there was an unecessary jump from 20mL to 200mL to 1000mL (x10 x5).