Ta có: 34,4x6,34+3,66x34,4
=34,4x(6,34+3,66)
=34,4x10
=344
Ta có: 17,2x9,55+12,45x17,2-17,2
=17,2x(9,55+12,45-1)
=17,2x21
Ta có: \(\frac{34,4\times6,34+3,66\times34,4}{17,2\times9,55+12,45\times17,2-17,2}\)
\(=\frac{344}{17,2\times21}=\frac{20}{21}\)

4 và 5