CPhill

There are 30 cars in my building's parking lot. All of the cars are red or white, and a car can have either 2 doors or 4 doors. 1/3 of them are red, 50% of them are 4-door, and 8 of them are 2-door and white. How many of the cars are 4-door and red?

10  are red.....so .....20 are white

15 are 4-door......so....15 are 2-door

8 are 2-door and white.....so.....12 must be 4-door and white since there are 20 white in total 

But......15 are 4-door....and 12 of these  are white....so.....

That must mean that  3 others are  4-door and red  

Thanks, hectictar.....I messed that first one up earlier...!!!

Here's the way I thought about this one :

http://web2.0calc.com/questions/help-plz-im-having-some-good-old-trouble-with-this-one#r1

Don't feel bad....we all feel like "half-wits" from time to time....LOL!!!!

To the best of my ability......answered here :

http://web2.0calc.com/questions/help_80357#r3

5x + 11 ≥  -9     subtract 11 to both sides    

5x ≥ -20       divide both sides by 5

x ≥ -4

10x  - 3  ≤  27     add 3 to both sides

10x ≤ 30      divide both sides by 10

x ≤  3

l  3x  +  1   l   =  1

We have two equations

3x +  1    =   1                                       3x  +  1   =   -1

                    subtract 1 from both sides

3x   =   0                                               3x  =  - 2

                   divide both sides by  3

x =  0                                                  x  =  -2 / 3

We can use any vowel  = 6 choices and any consonant  = 20 choices

And the vowel can come first or the consonant can come first  =  2 choices

So.....with one vowel we have  6 * 20 * 2  =  240 "words"

We can also use   a word with the same vowel repeated = 6 "words"

We can  also select any one of the vowels first  = 6 choices  and any one of the remaining vowels second  = 6 * 5  = 30 "words"

So......   240 +  6  +  30    =    276 "words"

-12x + 13y  = -10        we want to get y by itself

Add 12x to both sides

13y  =  12x  -  10       divide through by 13

y  =  (12/13)x  -  10/13     ⇒  slope (12/13), y intercept -10/13

4 - x + 20 = y - 10     simplify

24 - x  = y  - 10     rearrange as 

34  =  x + y

And  ( 4, 30)  ,  (24,10)   are the only solutions where x + y  =  34

y -  3  =  (4/7) ( x - 7)