Đổi: 75% = 3/4

Em có thể vẽ sơ đồ như sau: đáy 4 phần, chiều cao 3 phần, tổng là 42

=> Chiều cao hình tam giác là:

     42 : ( 3 + 4 ) x 3 = 18 (cm)

Độ dài đáy hình tam giác là:

    42 - 18 = 24 (cm)

Diện tích hình tam giác là:

   1/2 x 24 x 18 = 216 (cm vuông)

       Đ/s:..

23^2=529

đáp số: a=7 ; b=5 ; c=1 ; d=6

    4751 + 1367 = 5018

2

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             Bài giải 

11 quyển sách có số nghìn đồng là :

11 * 13000 =143000 ( đồng )

11 quyển vở có số nghìn đồng là :

11 * 5000 = 55000 ( đồng ) 

11 quyển sách ngiều hơn 11 quyển vở số nghìn đồng là :

143000 - 55000 = 88000 ( đồng ) 

                                      Đáp số : 88000 nghìn đồng       

=1500kg=150 yến=1,5 tấn

Đổi 25 % = 1/4

Tổng số phần bằng nhau là :

4 + 1 = 5 ( phần )

Độ dài chiều cao của khăn là :

80 : 5 = 16 ( cm)

Độ dài đáy của khăn là :

80 - 16 = 64 ( cm )

Diện tích của cái khăn là :

64 x 16 : 2 = 512 ( cm² )

Đáp số : 512 cm²

Gấp rưỡi = 1,5 = 3/2

35cm = 3,5dm

Tổng chiều dài và chiều rộng là:

17,5 x 2 : 3,5 = 10 (dm)

Đáy bé là:

10 : (3 + 2) x 2 = 4 (dm)

Đáp số : 4dm

10 + 8 = 18  là bội của 9

10² + 8 = 108  là bội của 9

10³ + 8 = 1008  là bội của 9

Vậy 10¹⁹⁹⁵ + 8 cũng là bội của 9