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Jul 9, 2023
Jul 8, 2023
 #1
avatar+2431 
0

 

The total surface area of a box is 100. The length of the box is twice its width, as well as 3 less than its height. How many units are in the height of the box?   

 

L = 2W        ——>    W = L / 2   

L = H – 3     ——>    H  = L + 3   

 

                                        Total Area  =  2 L W  +  2 L H  +  2 W H    

 

Substitute equivalent  

terms for W and H  

                                         A  =  (2)(L)(L/2)  +  (2)(L)(L + 3)  +  (2)(L/2)(L + 3)    

 

                                         A  =  2L2 / 2        +  2L2 + 6L        +  2L2 / 2 + 6L / 2  

 

                                         A  =  L2               +  2L2 + 6L         +  L2 + 3L    

 

                                         100  =  4L2  +  9L     

 

Rearrange as     

a quadratic     

                                         4L2  +   9L  –  100  =  0    

 

Factor                              (4L + 25)(L – 4)  =  0   

 

                                          4L = –25   Disregard.  A box can't have a negative length.   

 

                                            L = 4    

 

W = L / 2     ———>            W = 2   

 

H = L + 3     ———>            H = 7    

 

check answers    

                                         Total Area  =  2 • L • W  +  2 • L • H  +  2 • W • H    

 

                                                   100  =  (2)(4)(2)  +  (2)(4)(7)  +  (2)(2)(7)    

 

                                                   100  =  16   +  56  +  28    

 

                                                   100  =  100     

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Jul 8, 2023
 #1
avatar+2431 
0

 

One ordered pair (a,b) satisfies the two equations ab^4 = 48 and ab = 72. What is the value of b in this ordered pair?   

 

 

To find b, consider                                                  ab4  =  48  

 

We will divide both sides by ab.  

 

Since ab=72, we will divide the left side  

by "ab" and the right side by its equal 72.  

                                                                              ab4         48  

                                                                             ——   =   ——  

                                                                              ab           72  

Note that ab4 = (ab) * (b3)  

 

Cancel ab out of the left side.  

Reduce 48/72 on the right side.  

                                                                               b3           2  

                                                                             ——   =   ——  

                                                                                1            3  

 

 

                                                                                 b   =   cube root of (2 / 3)  

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Jul 8, 2023
Jul 7, 2023
 #3
avatar+2431 
0

 

Good catch, second guest.    

 

regarding      36/x + 8/(x^2) = 0  

                      Multiplying both sides of the equation by x2, we get:  

                      36 + 8x = 0   

 

Maybe if I write it like this,   

it will be easier to see   

                                                 36          8  

                                               ––––  +  ––––  =  0       

                                                  x            x2     

Multiplying both sides

by x2, we get    

                                                        36x  +  8  =  0   

 

                                                                36x  =  –8   

 

                                                                                8 

                                                                    x  =  – –––  =  – 2/9      

                                                                                36         

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Jul 7, 2023
 #1
avatar+2431 
0

 

Will and Grace are canoeing on a lake.  Will rows at 50 meters per minute and Grace rows at 20 meters per minute. Will starts rowing at 2 p.m. from the west end of the lake, and Grace starts rowing from the east end of the lake at 2 p.m. If they always row directly towards each other, and the lake is 3800 meters across from the west side of the lake to the east side, at what time will the two meet?   

 

Will's rate is 50 m/min.  

Grace's rate is 20 m/min.  

 

They're rowing toward each other,  

so their rate of closure is 70 m/min.  

 

The lake is 3800 meters across.  

 

The time it will take them to meet is given by  

                                                                                    Distance  

                                                                            T  =  –––––––  

                                                                                       Rate  

 

                                                                                    3800 m  

                                                                            T  =  –––––––  

                                                                                    70 m/min  

 

The time it takes them to meet                             T  =  54.29 min  

 

Note that (0.29 min • 60 sec/min)  =  17 seconds

 

The time on the clock is                                             2:54:17 pm 

.

Jul 7, 2023
 #2
avatar
+1

(a) Grogg's answer was probably arrived at by considering the two cases of exactly 4 A's and exactly 2 A's separately. For exactly 4 A's, there are (46​) ways to choose the 4 A's, and then 26 choices for each of the remaining two letters. For exactly 2 A's, there are (26​) ways to choose the 2 A's, and then 26 choices for each of the remaining four letters. So Grogg's answer is (46​)⋅262+(26​)⋅264.

 

(b) Grogg's answer is wrong because it does not account for license plates with 5 A's or 6 A's. There are (56​) ways to choose the 5 A's, and then 1 choice for the remaining letter, so there are (56​)=6 license plates with 5 A's. There is only 1 license plate with 6 A's. So Grogg's answer should be (46​)⋅262+(26​)⋅264+6+1. The correct answer is larger than Grogg's answer because Grogg's answer does not account for all the possible license plates.

 

(c) The correct answer to Ms. Q's problem is (46​)⋅262+(26​)⋅264+6+1=15⋅676+1560+7=26353. This is the number of license plates that contain exactly 4 A's, exactly 2 A's, 5 A's, or 6 A's.

Here is a more detailed explanation of how to solve the problem:

Case 1: Exactly 4 A's. There are (46​) ways to choose the 4 A's, and then 26 choices for each of the remaining two letters. So there are (46​)⋅262=15⋅676=10140 license plates with exactly 4 A's.

Case 2: Exactly 2 A's. There are (26​) ways to choose the 2 A's, and then 26 choices for each of the remaining four letters. So there are (26​)⋅264=1560 license plates with exactly 2 A's.

Case 3: 5 A's. There are (56​) ways to choose the 5 A's, and then 1 choice for the remaining letter. So there is 1 license plate with 5 A's.

Case 4: 6 A's. There is only 1 license plate with 6 A's.

The total number of license plates is 10140+1560+1+1=26353​.

Jul 7, 2023

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