lilai3 3 years ago PLEASE HELP!!!!!!!!!!!!!!!!!!!!!!!!!!! IT's about ALIENS :) Stephen wants to learn to communicate with the aliens so he spends lots of time with them. For a week he spends at least some time with then everyday. The number of days he spends time with them after noon is one more than the number he spends time with them before noon. The number of days he spends time with them only before noon is half as many as the number he spends time with them only after noon. How many days does he spend time with the aliens both before and after noon? PLEASE USE A VENN DIAGRAM TO SHOW WORK DONE. THX!

1. iNeedTheHelp

What does this have to do with math?

2. iNeedTheHelp

Ohhhh ok nevermind Here is the definition of a venn diagram: A Venn diagram is a diagram that uses circles to illustrate the relationships among sets. Example: The Venn diagram below shows the number of grade 5 students who scored above 50% on Math, above 50% on Science, and above 50% on both Math and Science. From the Venn diagram, we learn that 16 students scored above 50% on Math, 21 students scored above 50% on Science, and 6 students scored above 50% on both Math and Science.

3. lilai3

thanks, what a venn diagram is i just need to know how you solve this problem

4. ChmE

Are you there? I think I have the pieces we just need to put them together

5. lilai3

yes i'm here

6. ChmE

I am missing a number somewhere. I need to reread the question. there is only a total of 7 days!!

7. ChmE

a = b + 1 (a-c)/2 = (b-c) 7 = a + b - c These are our three equations

8. lilai3

? uhm i'm sorry i stll don't really get it... perhaps explain like what it's taking about cuz like i don't get the one more than the number stuff in the problem...

9. ChmE

Let a = total aliens after noon Let b = total aliens before noon Let c = # of aliens in both (a-c) is only after noon (b-c) is only before noon From the problem we have 2 equations we can write. a = b + 1 (a-c)/2 = (b-c) We have 2 equations and 3 unknowns so we still can't solve. We need another equation, a total equation. 7 = a + b - c

10. ChmE

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11. ChmE

a = b + 1 (a-c)/2 = (b-c) -> b = (a-c)/2 + c 7 = a + b - c Solve by substitution. 7 = ( b + 1) + b - c 7 = 2b + 1 - c 7 = 2[(a-c)/2 + c] - c 7 = a - c + 2c - c a = 7 b = 6 c = 6 That's a strange answer. I'm going to recheck my equations.

12. ChmE

I don't see a mistake. a = 7 days after noon b = 6 days before noon c = 6 days both

13. ChmE

14. lilai3

? uhm i'm sorry i stll don't really get it... perhaps explain like what it's taking about cuz like i don't get the one more than the number stuff in the problem...

15. ChmE

@hartnn can you double check this. My answer seems unlikely although I think my math is sound

16. ChmE

Okay we'll break down the wording first

17. ChmE

Let a = number after noon Let b = number before noon It is saying that he spends one more day with them after noon than before noon. Say b is 10. a would have to be 11 right? So we can write this equation b + 1 = a Plugging in our example to see if it works we get 10 + 1 = 11 11=11 check

18. ChmE

Do you understand that?

19. lilai3

sort of?

20. ChmE

What specifically confuses you about that explanation?

21. lilai3

the equation part

22. ChmE

We want something that represents what is happening. We use variables because we don't know what they are at first.

23. ChmE

If I told you I was 2 years older than you what equation would you write?

24. ChmE

your age + 2 = my age

25. ChmE

Is this helping?

26. lilai3

a little sorry my best subject isn't math

27. lilai3

oh like if my granpa was twice my age and i was like... 64 that would be 64 X 2 right?

28. lilai3

really bad example because grandpas are usually not that age compared to real life

29. ChmE

ya thats correct