Đề khảo sát học sinh giỏi lớp 6 số học (số tự nhiên)

 ĐỀ KHẢO SÁT HSG 6 SỐ HỌC (SỐ TỰ NHIÊN)
CÂU 1: Tìm dạng chung của số tự nhiên a sao cho n chia cho29 dư17 n chia cho 38 dư 27.
 Bài giải
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CÂU 2: CMR: Với mọi n lẻ thì: 
 2 
 n+ 4n+3 hết cho8	 
 Bài giải
........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................CÂU 3: Cho n có 39 ước . CMR: a, n là số chính phương
 b, Tích các ước của n viết 
 được dưới dạng a mũ 39 
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CÂU 4: Cho số 3 mũ 2016. Cho tổng chữ số của 3 mũ 2016 là A, tổng chữ số của A là B, tổng chữ số của B là C. Tìm C?
 Bài giải
.....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................CÂU 5:Tìm a,b biết:
a, BCNN( a,b ) + ƯCLN( a,b) = 55
b, a+b = 30 và BCNN(a,b) = 6.( a,b)
 Bài giải
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CÂU 6:Tìm hai số tự nhiên a và b biết : BCNN( a,b ) = 420, ƯCLN(a,b)=21 và a+21 = b
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