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Gọi số đó là: ab
Ta có:
ab : ( a + b ) = 7 ( dư 9 )
10a + b = 7(a+b) + 9
10a + b = 7a + 7b + 9
3a = b + 9
a = ( b + 9 ) : 3
Ta có các trường hợp:
TH1: b + 9 = 9
\(\Rightarrow\)a = 0 ; b = 0 ( loại vì a là hàng chục, không thể bằng 0 )
TH2: b + 9 = 18
\(\Rightarrow\)b = 9 ; a = 6 ( loại vì 69 : 15 = 4 ( dư 9 )
TH3: b + 9 = 27
\(\Rightarrow\)b = 18 ; a = 9 ( loại )
Tương tự bạn tìm các trường hợp tiếp theo
Giải :
Gọi X là chữ số hàng chục của số cần tìm (X là số tự nhiên và X>=1) "vì hàng chục ko có =0 đc"
Gọi Y là chữ số hàng đơn vị của số cần tìm (Y là số tự nhiên và Y>=0)
Vậy số cần tìm có dạng : 10X+Y
Theo đề bài ta có :
10X+Y = 7*(X+Y) + 9
<=> 3X - 6Y = 9
<=> X - 2Y = 3
<=> Y= (X-3):2
Vì Y>=0 => (X-3): 2 >=0 => X>=3
Ta có
X 3 4 5 6 7 8 9
Y - 1/2 1 3/2 2 5/2 3
Vậy các số đó là : 51; 72; 93
93 vì :
tổng của các chữ số trong số tự nhiên đó là:
9+3=12
kết quả của số tự nhiên đó chia cho tổng các chữ số của số đó là :
93/12=7(dư 9)
số tự nhiên đó là :93
Đáp số :số tự nhiên đó là 93
goi chu so hang don vi la b;so hang chuc la a
ab=(a+b)x7+9
ab=ax10+b
ax10+b=ax7+9
ax3=bx6+*
ax3=3x(bx2+3)
a=bx2+3(chia 2 ve cho 3)
ta co:b=1;a=5=>51(loai)
b=2;a=7=>72(loai)
b=3;a=9=>93
Vay so can tim la 93
ko thể dư 9 nhan bn ko bao giờ số dư lớn hơn số chia nha
Gọi số Cần tìm là ab .Theo đề bài ta có
ab=2x( a+b)+7
10 x a +b= a x 2 + b x 2 + 7 ( phân tích cấu tạo số )
10 x a +b - a x2 -b = a x2 + b x2 + 7-a x2 -b (cùng trừ a x2+b)
8xa = b + 7
Vì b<10 nên 8x a=b+7<10+7=17 và phải là một số chia hết cho 8
Vậy nếu 8xa=8 thì a=1 và b=1 có số 11 nhưng 11:(1+1)=5 dư 1 loại
Nếu 8xa=16 thì a=2 và b=9 có số 29:(2+9)=2 dư 7 lấy
Số Cần tìm là 29
Ta có: 10a + b = 2a + 2b + 7
8a = b + 7
Do 0<= b <= 9 nên 7<= 8a <= 16 nên a chỉ có thể là 1 hoặc 2.
a = 1, b = 1 , không thỏa mãn
a = 2, b = 9, thỏa mãn
Ta có: 10a + b = 2a + 2b + 7 8a = b + 7 Do 0<= b <= 9 nên 7<= 8a <= 16 nên a chỉ có thể là 1 hoặc 2. a = 1, b = 1 , không thỏa mãn a = 2, b = 9, thỏa mãn
Tìm một số tự nhiên có hai chữ số biết nếu lấy số đó chia cho tổng các chữ số của nó thì được 9 dư 1
gọi số đó là ab ta có :
ab = ( a + b ) x 9 + 1
10 x a + b = 9 x a + 9 x b + 1
a = 8 x b + 1
vì 0<a <9 hoặc =9 nên 8 x b + 1 < 9 hoặc = 9 vì a không thể là số có 2 chữ số
8 x b = 9-1
8 x b = 8
suy ra b =1 và a = 9
số đó là 91
93 nhé các bạn !!!!
93.Mình chắc luôn bạn
Cách làm sao vậy chỉ mình với
Cảm ơn mấy bạn. Tiện thể mk cũng tìm đc cách giải chi tiết luôn rồi. Số cần tìm có dạng 10a + b (a > 0, b >= 0), vậy theo đề bài thì ta có:
10a + b = 7(a + b) + 9
Đến đây thì giải như một bài tìm a, b thông thường.
10a + b = 7a + 7b + 9
10a - 7a = 7b - b + 9
3a = 6b + 9
6b + 9 = 3a
3a - 6b = 9
3a : 3 - 6b : 3 = 9 : 3 (Số trừ và số bị trừ cùng giảm đi bao nhiêu thì hiệu giảm đi bấy nhiêu)
a - 2b = 3
2b = a - 3
b = (a - 3) : 2
b = (a - 3) : 2
Vì b >= 0 nên (a - 3) : 2 >= 0.
=> a >= 3
=> a = 3; 4; 5; 6; 7; 8; 9
Nếu a = 3 thì b = (3 - 3) : 2 = 0 (Loại)
Nếu a = 4 thì b = (4 - 3) : 2 = 1/2 (Loại)
Nếu a = 5 thì b = (5 - 3) : 2 = 1
Nếu a = 6 thì b = (6 - 3) : 2 = 3/2 (Loại)
Nếu a = 7 thì b = (7 - 3) : 2 = 2
Nếu a = 8 thì b = (8 - 3) : 2 = 5/2 (Loại)
Nếu a = 9 thì b = (9 - 3) : 2 = 3
Vậy số cần tìm có thể là 51; 72; 93. (Trong 3 số này các bạn muốn lấy cái nào làm đáp án cuối cùng cũng đc)
93 la đung thât
93 nha
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