4.98×(10-0.1)+49.8=49.8+49.8-0.498+49.8=99.102
=4.98X10-4.98X0.1+4.98X10=49.8+49.8一0.498=99.6-0.498
4.98x9·9十49·8
=4.98x9·9十4.98*10
=4.98*(9.9+10)
=4.98*(20-0.1)
=99.6-0.498
=99.102
4.98换成49.8乘以0.99然后提取49.8乘（0.99➕1）
4.98×9＋4.98
=4.98×(9+1)
=4.98×10
=49.8
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