mình chỉ biết câu 1 thôi : 

lấy số bao gạo tẻ nhân với cân nặng của bao là 30 x 40 = 1200 kg.

sau đó ta cũng làm như cách kia là : 40 x 20 = 800 kg.

ta cộng 2 tích lại bằng : 1200 + 800 = 2000 kg

1. 

30 bao gạo tẻ nặng số ki-lô-gam là : 

40 x 30 = 1200 (kg)

40 bao gạo nếp nặng số ki-lô-gam là : 

20 x 40 = 800 (kg)

Xe đó chở số gạo là :

1200 + 800 = 2000  (kg)

2000kg = 2 tấn

Đáp số : 2 tấn

2.

1 tạ 50kg = 150 kg

Sau khi bán đi 25kg mỗi loại thì hiệu số gạo vẫn không đổi .

Lúc đầu cửa hàng có số gạo tẻ là :

150 : (5-2) x 5 = 250 (kg)

Lúc đầu cửa hàng có số gạo nếp là :

250 - 150 = 100 (kg)

Đáp số : 250kg gạo tẻ

               100kg gạo nếp

3.

a, \(\frac{41}{24}\)

b, \(\frac{194}{65}\)

Bài 3 mình ko chắc lắm.

Số kg gạo tẻ là:

50 x 32 = 1600 (kg)

Số kg gạo nếp là:

59 x 45 = 2655 (kg)

Vậy có tổng cộng:

1600 + 2655 = 4255(kg) = 4,255 tấn

ĐS: 4,255 tấn

Khối lượng của 30 bao gạo tẻ là:

30 x 40 = 1200 ( kg )

Khối lượng của 40 bao gạo nếp là:

40 x 20 = 800 ( kg )

Đổi : 1200 kg = 1,2 tấn

         800 kg = 0,8 tấn

Xe đó chở được số tấn gạo là:

1,2 + 0,8 = 2 ( tấn )

               Đáp số : 2 tấn gạo

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Số kg gạo tẻ là:

30.40=1200 (kg)

Số gạo  nếp là:

40.20=800 (kg)

Xe chở số tấn gạo là:

800+1200=2000(kg)

2000 kg=2 tấn

Đáp số : 2 tấn

T - N = 0,8 => T = N + 0,8

2/3 T = 4/5 N => 2/3 T - 4/5 N = 0 => 2/3 (N +0,8) - 4/5 N = 0

=> 2/3 N + 8/15 - 4/5 N = 0 

=> -2/15 N = -8/15 => N = 4 (kg)

T = N + 0,8 = 4 + 0,8 = 4,8 (kg)

Gạo tẻ: 4,8kg  Gạo nếp: 4kg( Tổng là : 8,8kg)

Lời giải:

a. Hiệu số phần bằng nhau:

$3-1=2$ (phần)

Số gạo tẻ là: $60:2\times 3=90$ (kg)

Số gạo nếp là: $90-60=30$ (kg)

b.

Buổi sáng bán được: $(90+30)\times \frac{2}{3}=80$ (kg)

Số gạo tẻ bán được là: $(80+40):2=60$ (kg)