`#040911`
`b,`
`6 \times 1235 \times 20 - 5 \times 235 \times 24`
`= 6 \times (1000 + 235) \times 20 - 5 \times 235 \times 24`
`= 120 \times 1000 + 120 \times 235 - 120 \times 235`
`= 120 \times 1000 + 0`
`= 120000`
`c,`
\((145 \times 99+145)-143 \times 101-143\)
`=`\(145 \times 99 + 145 - 143 \times 101 - 143\)
`=`\(145 \times (99 + 1) - 143 \times (101 - 1)\)
`=`\(145 \times 100 - 143 \times 100\)
`=`\(100 \times (145 - 143)\)
`=`\(100 \times 2=200\)
`d,`
`54 \times 47 - 47 \times 53 - 20 - 27`
`= 54 \times 47 - 47 \times 53 - (20 + 27)`
`= 54 \times 47 - 47 \times 53 - 47`
`= 47 \times (54 - 53 - 1)`
`= 47 \times 0=0`