Thống kê đồ ăn sáng của 35 học sinh lớp 7B ta thu được bảng sau:

Đồ ăn sáng	Số học sinh
Bánh mì	7
Cơm	3
Phở	12
Bún	12
Tổng cộng	34

Giá trị chưa hợp lí là:

1.

a) \(\left( {\frac{3}{5} - \frac{3}{4}x} \right):\frac{7}{5} = - \frac{1}{2}\)

\(\frac{3}{5} - \frac{3}{4}x = - \frac{1}{2}.\frac{7}{5}\)

\(\frac{3}{5} - \frac{3}{4}x = \frac{{ - 7}}{{10}}\)

\(\frac{3}{4}x = \frac{3}{5} - \frac{{ - 7}}{{10}}\)

\(\frac{3}{4}x = \frac{{13}}{{10}}\)

\[x = \frac{{13}}{{10}}:\frac{3}{4}\]

\[x = \frac{{26}}{{15}}\]

Vậy \[x = \frac{{26}}{{15}}\].

b) \(\left| {\frac{3}{2}x - \frac{1}{6}} \right| - {\left( {\frac{{ - 3}}{2}} \right)^2} = \frac{1}{3}\)

\(\left| {\frac{3}{2}x - \frac{1}{6}} \right| - \frac{9}{4} = \frac{1}{3}\)

\(\left| {\frac{3}{2}x - \frac{1}{6}} \right| = \frac{1}{3} + \frac{9}{4}\)

\(\left| {\frac{3}{2}x - \frac{1}{6}} \right| = \frac{{31}}{{12}}\)

Trường hợp 1: \(\frac{3}{2}x - \frac{1}{6} = \frac{{31}}{{12}}\)

\(\frac{3}{2}x = \frac{{31}}{{12}} + \frac{1}{6}\)

\(\frac{3}{2}x = \frac{{11}}{4}\)

\(x = \frac{{11}}{4}:\frac{3}{2}\)

\(x = \frac{{11}}{6}\)

Trường hợp 2: \(\frac{3}{2}x - \frac{1}{6} = \frac{{ - 31}}{{12}}\)

\(\frac{3}{2}x = \frac{{ - 31}}{{12}} + \frac{1}{6}\)

\(\frac{3}{2}x = \frac{{ - 29}}{{12}}\)

\(x = \frac{{ - 29}}{{12}}:\frac{3}{2}\)

\(x = \frac{{ - 29}}{{18}}\)

Vậy \(x \in \left\{ {\frac{{11}}{6};\,\,\frac{{ - 29}}{{18}}} \right\}\).

2.

a) \(A = \frac{7}{{38}}\,\,.\,\,\frac{9}{{11}} + \frac{7}{{38}}\,\,.\,\,\frac{4}{{11}} - \left| {\frac{{ - 7}}{{38}}} \right|\,\,.\,\,\frac{2}{{11}}\)\( = \frac{7}{{38}}\,\,.\,\,\frac{9}{{11}} + \frac{7}{{38}}\,\,.\,\,\frac{4}{{11}} - \frac{7}{{38}}\,\,.\,\,\frac{2}{{11}}\)

\( = \frac{7}{{38}}\,\,.\,\,\left( {\frac{9}{{11}} + \frac{4}{{11}} - \frac{2}{{11}}} \right)\)\( = \frac{7}{{38}}\,\,.\,\,\frac{{11}}{{11}}\)\( = \frac{7}{{38}}\).

b) \(B = \sqrt {\frac{{81}}{{25}}} \,\,.\,\,{\left( {\frac{{ - 5}}{3}} \right)^3} - \left| {\frac{{ - 12}}{7}} \right|:{\left( {\frac{{ - 3}}{7}} \right)^2} - \frac{{12}}{3}\)\( = \frac{9}{5}.\frac{{ - 125}}{{27}} - \frac{{12}}{7}:\frac{9}{{49}} - \frac{{12}}{3}\)

\( = \frac{9}{5}.\frac{{5.\left( { - 25} \right)}}{{9.3}} - \frac{{12}}{7}.\frac{{49}}{9} - \frac{{12}}{3}\)\( = \frac{{9.5.\left( { - 25} \right)}}{{5.9.3}} - \frac{{3.4.7.7}}{{7.3.3}} - \frac{{12}}{3}\)

\( = \frac{{ - 25}}{3} - \frac{{4.7}}{3} - \frac{{12}}{3}\)\( = \frac{{ - 65}}{3}\).

a) Vì \(\widehat {ADC} = 90^\circ \) nên đường thẳng \(c\) vuông góc với đường thẳng \(b\).

Ta có: \[a \bot c;\,\,\,b \bot c\]

Do đó \[a\parallel {\rm{b}}\] (quan hệ từ vuông góc đến song song).

b) Vì \(\widehat {{B_1}};\,\,\widehat {{B_2}}\) là hai góc kề bù nên \(\widehat {{B_1}} + \widehat {{B_2}} = 180^\circ \), \(\widehat {{B_2}} = 3\widehat {{B_1}}\), thay vào ta có:

\(\widehat {{B_1}} + 3\widehat {{B_1}} = 180^\circ \)

\(4\widehat {{B_1}} = 180^\circ \)

\(\widehat {{B_1}} = 180^\circ :4\)

\(\widehat {{B_1}} = 45^\circ \).

Lại có \[a\parallel {\rm{b}}\] nên \(\widehat {{B_1}}\) và \(\widehat {{C_1}}\) là hai góc đồng vị bằng nhau.

Do đó, \(\widehat {{C_1}} = 45^\circ \) hay \(\widehat {CDB} = 45^\circ \).