Là em cần giải chi tiết sao?

14c  15c  16b

Bài 14:

Để số đó nhân với \(\dfrac{7}{25},\dfrac{9}{35},\dfrac{11}{40}\)là tích các số TN thì số đó phải là BCNN(25,35,40)

25=5²

35=5.7

40=2³.5

BCNN(25,35,40)=5².2³.7=1400

Vậy số đó là 1400

Bài 16:

a) Ta có: \(A=-\dfrac{9}{5}\)

nên \(\dfrac{3x+9}{17-2x}=\dfrac{-9}{5}\)

\(\Leftrightarrow15x+45=-9\left(17-2x\right)\)

\(\Leftrightarrow15x+45+9\left(17-2x\right)=0\)

\(\Leftrightarrow15x+45+153-18x=0\)

\(\Leftrightarrow-3x=-198\)

hay x=66

b) Thay x=3 vào A, ta được:

\(A=\dfrac{3\cdot3+9}{17-2\cdot3}=\dfrac{18}{17-6}=\dfrac{18}{11}\)

Câu 14: B

Câu 15: A

B

A

B

A

Gọi số HS lớp 7A,7B,7C lần lượt là a,b,c(học sinh)(a,b,c∈N*,a,b,c<135)

Áp dụng t/c dtsbn:

\(\dfrac{a}{14}=\dfrac{b}{15}=\dfrac{c}{16}=\dfrac{a+b+c}{14+15+16}=\dfrac{135}{45}=3\)

\(\Rightarrow\left\{{}\begin{matrix}a=3.14=42\\b=3.15=45\\c=3.15=48\end{matrix}\right.\)

Vậy...

Gọi số học sinh lớp 7a, 7b,7c lần lượt là a,b,c

Ta có: \(\left\{{}\begin{matrix}\dfrac{a}{14}=\dfrac{b}{15}=\dfrac{c}{16}\\a+b+c=135\end{matrix}\right.\)

Áp dụng tcdtsbn ta có:

\(\dfrac{a}{14}=\dfrac{b}{15}=\dfrac{c}{16}=\dfrac{a+b+c}{14+15+16}=\dfrac{135}{45}=3\)

\(\dfrac{a}{14}=3\Rightarrow a=42\\ \dfrac{b}{15}=3\Rightarrow b=45\\ \dfrac{c}{16}=3\Rightarrow c=48\)

B nhé !

62 The more I think about the idea, the less attractive it becomes

63 The more slowly you walk, the longer it takes to get there

64 The less right you treat your disease, the more increasingly serious it will become

65 câu này thiếu dữ liệu roài

66 The newer the motorbike is, the less petrol it consumes

67 The more electricity you use, the higher your bill will be

68 The more books he reads, the more he knows about the word

69 The more I thought about , the more confused I became

70 The more problems arise, the less enthusiastic we feel

71 The more polluted the air is, the greater the chances of developing respiratory diseases are

72 The more popular TV programs become, the worse they seem to get

73 The less my boss is pressed for time, the worse he works

74 The more the economy grows, the better people's living conditions become

75 If you go to bed late, you will be tired

76 Unless you spend all your money, we can go on holiday

77 If you don't study, you won't pass your exams

78 Unless he smokes, the house won't smell bad

79 If you don't put your clothes away, your room will bea mess

80 If you don't go shopping, there won't be any food in the fridge

81 Unless you drink too much coffee, you can sleep

82 If you don't stop talking, you won't understand the lesson

83 If she studies hard, she will pass the exams

84 Unless we hurry up, we will be late for the meeting

85 If I had free time, I could help my mother with the housework

86 If he had his homework, he wouldn't be punished by the teacher

87 Unless he had a terrible headache, she wouldn't be absent from her class

88 If I knew her number, I would ring her up

89 Unless you rest yourself, you will be ill

90 Unless he ate so many chips, he wouldn't be fat