问题 解答题

用递等式计算(能简算的要简算).

102×4.5

7.8×6.9+2.2×6.9

5.6×0.25

0.654+10.9×6.5

8×(20-1.25)

4.2×1.5-2.74.

答案

①102×4.5,

=(100+2)×4.5,

=100×4.5+2×4.5,

=450+9,

=459;

②7.8×6.9+2.2×6.9,

=(7.8+2.2)×6.9,

=10×6.9,

=69;

③5.6×0.25,

=1.4×4×0.25,

=1.4×(4×0.25),

=1.4×1,

=1.4;

④0.654+10.9×6.5,

=0.654+70.85,

=71.504;

⑤8×(20-1.25),

=8×20-8×1.25,

=160-10,

=150;

⑥4.2×1.5-2.74,

=6.3-2.74,

=3.56.

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