Math Questions iin OG 10th Edition - help

siqizhang

Hi Guys,

I have some questions in math problem solving in OG 10TH edition

question 176,
1,234
1,243
1,324
..........
..........
+4,321
----------


The addition problem above shows four of the 24 different integers that can be formed by using each of the digits 1,2, 3, and 4 exactly once in each integer. What is the sum of these 24 integers?
A. 24,000  B. 26,664, C. 40,440, D. 60,000  E. 66,660

The answer is E  (Don't quite understand why)

Question 189. If a positive integer N is divisible by both 5 and 7, the N must also be divisible by which of the following?
I. 12
II. 35
III. 70

A. NON, B. I only  C. II ONLY  D. I and II   E. II and III

The answer is C.  ( I don't understand why it is not E)

Thank you for the explanation, guys

zwjb828

You are welcome.

siqizhang

Well... In my opinion, the question tells us that this number has at least two prime factors, 5 &7. We can not make sure whether this number has  another prime factor, i.e. 2,  as well.

-- by 会员 zwjb828 (2010/6/15 16:42:33)

That's a genius point !!! I think I got it. Thank you !

zwjb828

Well... In my opinion, the question tells us that this number has at least two prime factors, 5 &7. We can not make sure whether this number has  another prime factor, i.e. 2,  as well.

siqizhang

But in Question 189, they did not ask for Even or Odd numbers at the beginning, I don't quite understand why in answers, they only pick up an Odd number 35 as the answer, which is very strange to me.

Thank you for your help

zliycdr

176题：由题意，1，2，3，4各在个十百千位上出现六次，所以和应该是（1+2+3+4）*6*（1+10+100+1000）
189题：没有说N是偶数，只说是正数，所以不选E

-- by 会员 jiaman1011 (2010/6/14 21:22:00)

So... zhengque daan shi yi a... wo cuole... yiwei shi si

jiaman1011

176题：由题意，1，2，3，4各在个十百千位上出现六次，所以和应该是（1+2+3+4）*6*（1+10+100+1000）
189题：没有说N是偶数，只说是正数，所以不选E

nowwsy

额。。弄错了。。正在看题。。

zliycdr

diyibaibashijiutiwoyejuedeshicei weishenmeshiyiya? qiugaorenzhidian!

zliycdr

wo yingyu butaihao beijuya...