选择合适的方法用递等式计算下列各题。7.6×2.5×0.4 99×88+99

20﹣12÷ $\text{[math]}$

脱式计算未知容易

2. $\text{[math]}$

脱式计算未知容易

$\text{[math]}$ ×40=	$\text{[math]}$ ÷ $\text{[math]}$ =	$\text{[math]}$ × $\text{[math]}$ =
$\text{[math]}$ ×2.1=	0÷ $\text{[math]}$ =	20×45%=
25%÷ $\text{[math]}$ =	1÷ $\text{[math]}$ × $\text{[math]}$ =	$\text{[math]}$ × $\text{[math]}$ ÷ $\text{[math]}$ × $\text{[math]}$ =