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6. 要使$2.3×a +7.7×a=4.06$，这里的a是(
A.4.06
B.40.6
C.0.0406
D.0.406
D
)。A.4.06
B.40.6
C.0.0406
D.0.406
答案
6. D
三、算一算。
1.直接写得数。
$3.2×0.3=$ $0.04×0.02=$ $1.5×0.2=$ $7.8×0.1=$
$9.5-0.5×2=$ $2.5×0.4=$ $1.25×8=$ $0.3×0.3=$
$0.05×20=$ $12.5-2.5×4=$
1.直接写得数。
$3.2×0.3=$ $0.04×0.02=$ $1.5×0.2=$ $7.8×0.1=$
$9.5-0.5×2=$ $2.5×0.4=$ $1.25×8=$ $0.3×0.3=$
$0.05×20=$ $12.5-2.5×4=$
答案
1. 0.96 0.0008 0.3 0.78
8.5 1 10 0.09 1 2.5
8.5 1 10 0.09 1 2.5
2.列竖式计算，带*的需要验算。
0.83×3.2=
2.7×5.1≈
（得数保留一位小数）
2. 6×0.25=
0.83×3.2=
2.7×5.1≈
（得数保留一位小数）
2. 6×0.25=
答案
2. 0.83×3.2=2.656 2.7×5.1≈13.8
2.6×0.25=0.65
验算 
3.计算下面各题，能简算的要简算。
0.25×9.2×0.4
9.6+0.4×55
3.6×101
5.2×7−3.2×0.7
0.25×9.2×0.4
9.6+0.4×55
3.6×101
5.2×7−3.2×0.7
答案
解：
3. 0.25×9.2×0.4
=(0.25×0.4)×9.2
=0.1×9.2
=0.92
9.6+0.4×55
=9.6+22
=31.6
3.6×101
=3.6×(100+1)
=3.6×100+3.6×1
=360+3.6
=363.6
5.2×7−3.2×0.7
=52×0.7-3.2×0.7
=0.7×（52-3.2）
=0.7×48.8
=34.16
