QR - Destroyer - Counting Numbers

[belmont3]

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Regina and Steven play a game. They begin counting starting from 1. If the number is even Regina places a penny on the table. If the number is prime, Steven puts a penny on the table. How many pennies are placed on the table if they count from 1 to 10?

a) 1
b) 7
c) 8
d) 9
e) 10

I know the answer should be between c and d, but I'm not sure which one is the correct answer. I'm not sure if they put 2 pennies when they get the number 2; since 2 is a prime number and an even number? Thank you!

 

[NLP26]

For problems like this, I usually like to go through one by one. 10 is a relatively small number so it shouldn't take you long.

So for 1... that's prime (net result = 1 penny down)
2... prime and even (net result = 2 pennies down)
3... prime (= 1 penny down)
4... even (= 1 penny down)
5... prime (= 1 penny down)
6... even (= 1 penny down)
7... prime (= 1 penny down)
8... even (= 1 penny down)
9... neither (=0 pennies down)
10... even (= 1 penny down)

add all that up... you get 10.

 

[KyoPhan]

Pretty sure they will place 2 pennies for the number 2.

And how are u getting between c and d. I'm counting 9-10 depending on if 2 is included or not. What does the answer say?

 

[belmont3]

Actually, I don't have the answers with me. However, I think the answer is D; since 1 is not a prime number. It only divides on itself. I just wasn't sure if we should count 2 pennies when they get number 2 or not.

 

[NLP26]

Actually, I don't have the answers with me. However, I think the answer is D; since 1 is not a prime number. It only divides on itself. I just wasn't sure if we should count 2 pennies when they get number 2 or not.

Good call, completely forgot about that.

 

[KyoPhan]

Oh, I didn't know that 1 wasn't a prime. I think they would have to add another sentence if only 1 can be placed for 1 number.

 

[dontbescared]

Did this question recently. Yes, 1 is not prime, and the answer is 9.