4.2×3=4.2+4.2+4.2.
正確
分析:小數(shù)乘整數(shù)的意義同整數(shù)乘法的意義相同,都是求幾個(gè)相同加數(shù)和的簡(jiǎn)便運(yùn)算.據(jù)此解答.
解答:4.2×3表示的意義是3個(gè)4.2是多少,所以4.2×3=4.2+4.2+4.2.
故答案為:正確.
點(diǎn)評(píng):本題主要考查了學(xué)生對(duì)小數(shù)乘整數(shù)意義的掌握情況.
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雞兔同籠,有頭10個(gè),腿32條.雞、兔各幾只?
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頭/個(gè) 10 10 10 10 10 10 10 10 10
兔/只 1 2 3 4 5 6 7 8 9
雞/只 9 8 7 6 5 4 3 2 1
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(2)用假設(shè)法解:
①假設(shè)籠子里全是雞,那么就有
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條腿,這樣就比原來(lái)的總腿數(shù)少了
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條,這是由于每把一只兔變成一只雞就要少
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條腿的緣故.根據(jù)上面兩個(gè)數(shù)就可求出兔有
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只,綜合算式是
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②假設(shè)籠子里全是兔,那么就有
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條腿,這樣就比原來(lái)的總腿數(shù)多了
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條腿,這是由于每把一只雞變成一只兔就要多
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條腿的緣故.根據(jù)上面這兩個(gè)數(shù)據(jù)就可求出雞有
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只,綜合算式是
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(3)用方程解:
①設(shè)雞有x只,那么兔就有
10-x
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只,則根據(jù)數(shù)量關(guān)系即可列出方程:
2x+4(10-x)=32
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②設(shè)兔有x只,那么雞就有
10-x
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只,則根據(jù)數(shù)量關(guān)系即可列出方程:
4x+2(10-x)=32
4x+2(10-x)=32

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