(1992+1/2)-(1+1/3)+(2+1/2)-(3+1/3)+(4+1/2)-(5+1/3)+......+(1990+1/2)-(1991+1/3)= (1992-1+2-3+4+5+......+1990-1991) + (1/2+1/2+1/2+......1/2)-(1/3+1/3+1/3+......1/3)= 1×(1992÷2) + (1/2)×(1992÷2) - (1/3)×(1992÷2)= 996 + 498 - 332= 1162