=(6+4)+(8-1-7)+(3+9-2)
=10+0+10
=10+10
=20
3 + 8 - 1 + 6 - 7 + 9 - 2 + 4
=(6 + 4 ) + (8 - 1 - 7) + (3 + 9 - 2)
=10 + 0 + 10
=20
3 + 8 - 1 + 6 - 7 + 9 - 2 + 4
= 11 - 1 + 6 - 7 + 9 - 2 + 4
= 10 + 6 - 7 + 9 - 2 + 4
= 16 - 7 + 9 - 2 + 4
= 9 + 9 - 2 + 4
= 18 - 2 + 4
= 16 + 4
= 20
3+8-1+6-7+9-2+4
=( 8-7-1 ) + ( 9+3-2 ) + ( 6+4 )
=0+10+10
=20