Số hoàn hảo là số mà tổng các ước của nó bằng 2 lần chính nó.

Ví dụ: 6 là số hoàn hảo vì 6 có tổng ước là 1+2+3+6=12=2 lần 61+2+3+6=12=2 lần số là số hoàn hảo vì 6
1

Yêu cầu: Viết chương trình nhập vào số nguyên n. In ra chữ YES nếu n là số hoàn hảo, ngược lại ghi chữ NO

Viết đoạn văn ngắn 5-7 câu để trả lời câu hỏi: Cần làm gì khi phải đối đầu với kẻ mạnh?

Dấu hiệu để nhận biết kiểu văn bản tự sự (nhân vật, không gian, thời gian)?

Vì sao tròn trồng trọt nên trồng cây với mật độ phù hợp.

Complete the dialogue. Use the present perfect with just, already and yet.

Vicky:     (►) You haven’t done your project yet (you / not do / your project / yet), I suppose.

Rachel:   No, I haven't. (1) (I / not / start / it / yet).

Vicky:     (2)............ (I /just / see / Andrew), and he says

(3) (he / already / do) about half of it.

Rachel:   Well, he works too hard.

Vicky:     (4) (I / not / finish / my plan / yet).

Rachel:   (5) (you / already / begin) to worry about it, haven't you?

Take it easy. There's plenty of time.
Vicky:     (6) (we / already / spend) too long thinking about it.

(7) (I / not / do / any real work / yet)

and (8) (I / just / realize) that there are only four weeks

1  to the end of term.
Rachel:   OK. (9) (I / just / decide) to start next week. Well, maybe.

Trevor and Laura are decorating their house. Put in the verbs. Use the present perfect.

Laura:    How is the painting going? (►) Have you finished ? (you / finish)

Trevor:    No, I haven't. Painting the ceiling is really difficult, you know. (1) (I / not / do) very much. This new paint (2) (not / make) any difference.

Laura:     (3)      (you / not / put) enough on.

Trevor:    (4)    (I / hurt) my back. It feels bad.

Laura:     Oh, you and your back. You mean (5) (you / have) enough of decorating. Well, I'll do it. Where (6) (you / put) the brush?

Trevor:    I don't know. (7) (it / disappear).

(8) (I / look) for it, but I can't find it.

Laura:    You're hopeless, aren't you? How much (9) (you / do) in here? Nothing! (10) (I / paint) two doors.

Trevor:    (11) (I / clean) all this old paint around the window.

It looks much better now, doesn't it?
Laura:     (12) (we / make) some progress, I suppose.

I.             Add a sentence. Use the present perfect.

► I'm tired. (I / walk / miles) I've walked miles.

1  Emma's computer is working now. (she / repair / it)

2  It's cooler in here now. (I / open / the window)

3  The visitors are here at last, (they / arrive)

4  Mark's car isn't blocking us in now. (he / move / it)

5  We haven't got any new videos, (we / watch / all these)