4: The sum of all positive integers less than or equal to 500 which are not multiples of 7

Firstly, the sum of 1 to 500 is (1+500)/2 (the average) times 500 = 125250

Then, all multiples of 7 are 7 to 497, and there are 71 of them. Their sum is (497+7)/2 (the average) times 71 = 17892

125250 - 17892 = 107358

I think

]]>Problems 2 is easy and I can solve them. But other problems left, I can't......

Problem 4: how do you form that? Pls.

]]>2. (B) Given f(x)=x²+1 is x is greater than or equal to 2. In this case, x=2.

4. (D) Use the formula for n(n+1)/2 for n=500 and then subtract 71/2{14+490}from it.

19.(C)

I shall try the others later....:)]]>

I'm a Vietnamese and I intend to apply for an exam call Entrance Examination, of National University of Singapore. As you see, the problems are written in English and too difficult for me to do (except some easy problem which I can solve).

I hope that someone would help me to solve these problems.

Thanks in advance.

]]>www.nus.edu.sg/oam/doc/uee/math.pdf

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