Giải: 

Có số gạo dự trữ là: 120\(\times\)20=2400(kg)

Số gạo đó đủ cho 100 người ăn trong số ngày là: 2400:100=24 (ngày)

Đáp số: 24 ngày

ab=ba.3+13

=>a.10+b=(b.10+a).3+13

=>a.10+b=b.30+a.3+13

=>a.10-a.3=b.30-b+13

=>a.7=b.29+13

Xét b=0=>a.7=0.29+13

=>a.7=13

=>a=13/7

=>Vô lí.

Xét b\(\ge\)1=>b.29\(\ge\)29=>b.29+13\(\ge\)42

=>a.7\(\ge\)42

=>a\(\ge\)6

Với a=6=>a.7=42=b.29+13=>b.29+13=42=>b.29=29=>b=1

Với a=7=>a.7=49=b.29+13=>b.29+13=49=>b.29=36=>b=36/29(vô lí)

Với a=8=>a.7=56=b.29+13=>b.29+13=56=>b.29=43=>b=43/29(vô lí)

Với a=9=>a.7=63=b.29+13=>b.29+13=63=>b.29=50=>b=50/29(vô lí)

Vậy ab=16

Talking about school subjects / schedulesand regulations

Làm ơn giúp mk với . Mk cần gấp

1. When does she go to work ?

2.Her favorite food is noodles.

3. How much are these apples cost ?

4. It is a blue car.

16y²-x²-2x-1

=16y²-(x²+2x+1)

=(4y)²-(x+1)²

=[4y-(x+1)][4y+(x+1)]

=(4y-x-1)(4y+x+1)

The kind of traditional Vietnamese performance I know are puppet show, folk msic, ca tru, cheo, xam, ......

You are late for school

The most popular activity at recess is chatting

Tim is the same age as Hoa

1. What does she do ?

2. I am a student and this is my school .

3. Is that your eraser .

4. There are twenty students in Mai s class

5. Where is my book ?