Math Is Fun Forum

atut

Member

Registered: 2008-04-23

Posts: 30

hi

I just dont understand this question.....

Write each of the following numbers as a product of its prime factors:

78,                                     240,                                           420.

Answers: 78 = ---------

240 = -------

420 = --------

:):|:(:D:o;):/:P:lol::mad:::cool:

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: hi

For this question, you find a group of prime numbers that multiply to give the original number. The easiest way to do this is to find one prime number at a time:

78
2 x 39
2 x 3 x 13

2, 3 and 13 are all prime, so that is the answer.

(You could have had 3 x 26 in the middle if you'd taken out the 3 first, but no matter what order you do things in, the final answer will always be the same)

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Why did the vector cross the road?
It wanted to be normal.

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 48,045

Re: hi

240 = 2 x 120
240 = 2 x 2 x 60
240 = 2 x 2 x 2 x 30
240 = 2 x 2 x 2 x 2 x 15
240 = 2 x 2 x 2 x 2 x 3 x 5

This is how the number 240 is written as a product of prime numbers.
Try the third one yourself.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.