978 x 8,76 + 8,76 + 8,76 x 21
= 8,76 x ( 978 + 1 + 21 )
= 8,76 x 1000
= 8760
\(9,78x8,76+8,76+8,76x21\)
\(=9,78x8,76+8,76x1+8,76x21\)
\(=8,76x\left(9,78+1+21\right)\)
\(=8,76x31,78\)
\(=278,3928\)
Mình nghĩ là vậy
9,78.8,76+8,76+8,76.21=8,76.(9,78+1+21)=8,76.31,78=278,3928