\(\dfrac{1978.1979+1980.21+1958}{1980.1979-1978.1979}\)
\(=\dfrac{1978.1979+\left(1979+1\right).21+1958}{1979.\left(1980-1978\right)}\)
\(=\dfrac{1978.1979+1979.21+21+1958}{1979.2}\)
\(=\dfrac{1978.1979+1979.21+1979.1}{1979.2}\)
\(=\dfrac{1979.\left(1978+21 +1\right)}{1979.2}\)
\(=\dfrac{1978+21+1}{2}=\dfrac{2000}{2}=1000\)
\(\dfrac{1978.1979+1980.21+1958}{1980.1979-1978.1979}\)
\(=\dfrac{1978.1979+1979.21+21+1958}{1980.1979-1978.1979}\)
\(=\dfrac{1979\left(1978+21\right)+21+1958}{1979\left(1980-1978\right)}\)
\(=\dfrac{1978+21+21+1958}{1980-1978}\)
\(=\dfrac{3978}{2}\)
\(=1989\)
