7分之12—（7分之5+2分之1）
=12/7-5/7-1/2
=7/7-1/2
=1-1/2
=1/2
[1—（4分之1+8分之3）]除以4分之1
=（1-1/4-3/8）x4
=1x4-1/4x4-3/8x4
=4-1-3/2
=3-3/2
=3/2
=1又1/2
8分之1 x 58+8分之1 x 42
=1/8x(58+42)
=1/8x100
=100/8
=12又1/2
5分之4 x 7分之4 x 4分之5—3分之1
=4/5x5/4x4/7-1/3
=1x4/7-1/3
=4/7-1/3
=12/21-7/21
=5/21
9分之5 x 6+9分之4除以6分之1
=5/9x6+4/9x6
=(5/9+4/9)x6
=9/9x6
=1x6
=6
180除以2.5除以4
=180÷(2.5x4)
=180 ÷10
=18
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