Math Games

Archive for October, 2008

Question: math help, please help?

i was absent in school and missed a few lessons. i got a worksheet from school to do at home but i have no clue what to do. can some one help me please. thank you.

what are the last two digits(tens and units) of the product of all positive prime numbers less than 100?

katelyn and carly are playing a game that uses ten cards numbered 1 to 10 that are faced on a table. if katelyn and carly each turn over one card, what is the probability that the sum of the two cards is even?

thanks to everyone who can answer!
i dont get how u got 70 for the first one

Answer: I think the last digits are 70. It must end with zero since 2x5 = 10 and 2 and 5 are primes. I got the 7 by multiplying the primes and keeping track of the second digit by periodically removing the last two digits from the products.

That probability boils down to the chance of getting either two odds or two evens. There are 5 odds and 5 evens in 1 through 10, so the chances of getting both odds is

5/10 x 4/9 = 20/90

The chance of getting both even is

5/10 x 4/9 = 20/90

And the chance that the sum is even is 20/90 + 20/90 = 40/90

Or 4/9.

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