Các phân số được sắp xếp theo thứ tự tăng dần là: \(\dfrac{1}{4};\dfrac{2}{5};\dfrac{1}{2};\dfrac{3}{5};\dfrac{2}{3}\)

 Đổi: 18dm = 1,8m

      Thể tích của bể cá là:

              1,6 x 1,25 x 1,8 = 3,6 ( m3 ) = 3600  \(dm^3\)

         Thể tích của thùng hình hộp chữ nhật là:

              5 x 3 x 4 = 60 ( dm3 )

      Phải đổ nước vào bể số lần là:

               3600 : 60 = 60 ( lần )

                               Đáp số: 60 lần

\(\dfrac{1}{4}+\dfrac{75}{100}+\dfrac{1}{5}+\dfrac{100}{125}\)

\(=\dfrac{1}{4}+\dfrac{3}{4}+\dfrac{1}{5}+\dfrac{4}{5}\)

= 1+ 1

= 2

62

Dọc theo chiều dài, ta trồng được:

$5.5:\frac{1}{4}=22$ (khóm hoa)

Dọc theo chiều rộng, ta trồng được:

$3,75:\frac{1}{4}=15$ (khóm hoa)

Như vậy, số khóm hoa trồng được dọc theo hai cạnh của mảnh vườn là:

$\left[\right(22+15\left).2\right]-4=70$ (khóm hoa)

Đáp số: 70 khóm hoa

a) $\frac{1}{5}+\frac{4}{5}:x=0,75$

$\frac{1}{5}+\frac{4}{5}:x=\frac{3}{4}$

$\frac{4}{5}:x=\frac{3}{4}-\frac{1}{5}$

$\frac{4}{5}:x=\frac{11}{20}$

$x=\frac{16}{11}$;

b) $x+\frac{1}{2}=1-x$

 $2x=1-\frac{1}{2}$

 $2x=\frac{1}{2}$

 $x=\frac{1}{4}$.

a) $\frac{2}{3}\cdot \frac{5}{4}-\frac{3}{4}\cdot \frac{2}{3}=\frac{2}{3}\cdot \left(\frac{5}{4}-\frac{3}{4}\right)=\frac{2}{3}\cdot \frac{1}{2}=\frac{1}{3}$;
b) $2\cdot {\left(\frac{-3}{2}\right)}^2-\frac{7}{2}=2\cdot \frac{9}{4}-\frac{7}{2}=\frac{9}{2}-\frac{7}{2}=1$;
c) $-\frac{3}{4}\cdot 5\frac{3}{13}-0,75\cdot \frac{36}{13}=-\frac{3}{4}\cdot 5\frac{3}{13}-\frac{3}{4}\cdot \frac{36}{13}$
$=-\frac{3}{4}\left(5\frac{3}{13}+\frac{36}{13}\right)$
$=-\frac{3}{4}\cdot 8=-6$.

$a,\frac{2}{3}.\frac{5}{4}-\frac{3}{4}.\frac{2}{3}=\frac{2}{3}.\left(\frac{5}{4}-\frac{3}{4}\right)=\frac{2}{3}.\frac{2}{4}=\frac{1}{3}$

$b,2.\left(\frac{-3}{2}\right)-\frac{7}{2}=-6.\frac{1}{2}-7.\frac{1}{2}=\left(-6-7\right).\frac{1}{2}=-13.\frac{1}{2}=\frac{-13}{2}$

$c,-\frac{3}{4}.5\frac{3}{13}-0,75.\frac{36}{13}=-\frac{3}{4}.\left(\frac{68}{13}-\frac{36}{13}\right)=-\frac{3}{4}.\frac{32}{13}=-\frac{24}{13}$

1. He (work) _is working_in the office now.
2. My friend (enjoy)_enjoys hamburgers very much.
3. The students ( look)are looking up these new words right now.
4. We always (do) _do_ English exercises carefully.
5. The sun (rise) rises__ in the east.
6. They (talk) _are talking_ to John at the moment.
7. The children (sleep) _sleep__ well for two hours every afternoon.
8. My sister (need) _needs__ some money for books.
9. It (rain) rains very much in the United States.
10. Linda (write) _is writing to David at the moment.
11. Thu (not have) does not have any apples. She (have) has some oranges.
12. Minh (watch)  watches  TV every night. he (watch)  is watching  TV at present.
13. We often (swim) swim  in the river, but today we (go)  are going  fishing.
14. They often (play) play tennis. They (play)  are playing  tennis at the
moment.
15. Nam (ride)  rides  his bike to school everyday, but now he (walk) is walking  to school.

Theo đề bài, ta có

 \(\dfrac{99+m}{137+m}\)=\(\dfrac{3}{4}\)

⇔ 4( 99+m) =3( 137+m) ⇔ 396+4m= 411+3m⇔4m-3m=411-396

=>  m=15