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Arithmetic, number property test

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Arithmetic, number property test

by pjmulder » Sun Dec 04, 2011 2:57 pm
I have a problem which I cannot solve or the answer is wrong. P32 Kaplan math

How many positive integers less than 60 are equal to the product of a positive multiple of 5 and an even number?

my answer was: 9
10 * 5
8 * 5
6 * 5
4 * 5
2 * 5

4 * 10
2 * 10

2 * 15

2 * 20

The answer according to the book is 5.

"Here we want to determine, basically, how many numbers between 0 and 60 are even multiples of 5. Well, all even multiples of 5 must be multiples of 10. So the multiples of 10 between 0 and 60 are 10, 20, 30, 40 and 50. That's 5."

Am I reading this wrong? They ask for "positive multiples of 5", but in the answer we're suddenly looking for "even multiples of 5"?
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by chieftang » Sun Dec 04, 2011 4:09 pm
pjmulder wrote:I have a problem which I cannot solve or the answer is wrong. P32 Kaplan math

How many positive integers less than 60 are equal to the product of a positive multiple of 5 and an even number?

my answer was: 9
10 * 5
8 * 5
6 * 5
4 * 5
2 * 5

4 * 10
2 * 10

2 * 15

2 * 20

The answer according to the book is 5.

"Here we want to determine, basically, how many numbers between 0 and 60 are even multiples of 5. Well, all even multiples of 5 must be multiples of 10. So the multiples of 10 between 0 and 60 are 10, 20, 30, 40 and 50. That's 5."

Am I reading this wrong? They ask for "positive multiples of 5", but in the answer we're suddenly looking for "even multiples of 5"?
It's 5. You have duplicates in your list.

Example, you have 4*10 and 8*5 which give the same number.
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by user123321 » Sun Dec 04, 2011 4:29 pm
The numbers below 60 which are +ve & divisible by even multiple of 10 are....
10,20,30,40,50 = 5 numbers

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by neelgandham » Mon Dec 05, 2011 5:43 am
pjmulder wrote: my answer was: 9
10 * 5= 50
8 * 5 = 40
6 * 5 = 30
4 * 5 = 20
2 * 5 = 10
4 * 10= 40
2 * 10= 10
2 * 15= 30
2 * 20= 40

The answer 9 would(or may) be correct if the question posed is In how many ways, positive integers less than 60 can be written as a product of a positive multiple of 5 and an even number?. Here the question is How many positive integers less than 60 are equal to the product of a positive multiple of 5 and an even number? and the answer is 5 - 10,20,30,40,50. The only mistake committed is counting the duplicates(marked in the same color in the list above)
Am I reading this wrong? They ask for "positive multiples of 5", but in the answer we're suddenly looking for "even multiples of 5"?
Again, the question reads How many positive integers less than 60 are equal to the product of a positive multiple of 5 and an even number? . So, a number which can be written as a multiple of 5 and an even number(2 or 4 or 6) can also be written as a multiple 10 and another number(5*even number = 5*(2 or 4 or 6) = 10*(1 or 2 or 3))

Hope it helps!
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by LalaB » Mon Dec 05, 2011 9:42 am
first, i wrote down all multiples of 5-

5 10 15 20 25 now stop! because the next number is 30 .if u multiply 30 to 2 (even number), u will get 60,which is not less than 60

so, now we see that we have only 5 numbers.
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