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 #1
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If I give my brother 5 dollars, then we will have the same amount of money. If instead he gives me 25 dollars, then I'll have twice as much money as he will have. How much money does my brother currently have (in dollars)?    

 

Call M the amount currently held by Me   

Call B the amount currently held by Brother   

 

                                                             (M – 5)  =  (B + 5)               (eq 1)   

 

                                                             (M + 25)  =  2 • (B – 25)      (eq 2)   

 

Multiply (2) out                                        M + 25  =  2B – 50   

Multiply both sides of (1) by 2               2M – 10  =  2B + 10    

Subtract                                                –M + 35  =       – 60   

Combine like terms                               –M           =       –95     

Multiply both sides by –1                                  M  =  95   

 

Plug value of M into (1)                             95 – 5  =  B + 5  

Combine like terms                                          85  =  B    

 

My Brother currently has 85 dollars   

 

check answer  

 

Plug 95 and 85 into (2)                            (95 + 25)  =  (2)(85 – 25)   

                                                                         120  =  2 • 60   

                                                                         120  =  120  

.

Jul 7, 2023
 #1
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In Linguistics 101, the ratio of the number of juniors to the number of seniors is 3:2.  When six more juniors join the class, and one senior drops the class, the ratio of the number of juniors to the number of seniors becomes 2:3.  How many students are in the class after these changes?   

 

I can tell you immediately that increasing the number     

of juniors will not invert the ratio.  But I'll go through    

the motions for you anyway.     

 

                                                       J          3   

                                                      ––   =   ––  

                                                       S          2     

 

                                                   J + 6          2   

                                                   ––––   =   –––   

                                                   S – 1          3        

 

Cross multiply both                            2J  =  3S            (eq 1)  

                                                  3J + 18  =  2S – 2      (eq 2)      

 

Get either J or S in terms of the   

other.  It doesn't matter which,   

but J would be simpler.                       J  =  3S/2      

 

Substitute this in eq 2                (3) • (3S/2) + 18  =  2S – 2    

 

                                                        9S/2 + 18  =  2S – 2     

 

Multiply both sides by 2                      9S + 36  =  4S – 4    

 

Subtract 4S from both sides               5S + 36  =  –4   

 

Subtract 36 from both sides                    5S  =  –40     

 

You cannot have a negative number of seniors    

so something is wrong somewhere.  The error     

is in the initial proposition.  This problem has ...... no solution.    

.

Jul 7, 2023
 #1
avatar+1277 
0

 

If I give my brother 5 dollars, then we will have the same amount of money. If instead he gives me 25 dollars, then I'll have twice as much money as he will have. How much money does my brother currently have (in dollars)?    

 

Call M the original amount held by Me   

Call B the original amount held by Brother   

 

                                                             (M – 5)  =  (B + 5)               (eq 1)   

 

                                                             (M + 25)  =  2 • (B – 25)      (eq 2)   

 

Multiply (2) out                                        M + 25  =  2B – 50   

Multiply both sides of (1) by 2               2M – 10  =  2B + 10    

Subtract                                                –M + 35  =       – 60   

Combine like terms                               –M           =       –95     

Multiply both sides by –1                                 M  =  95   

 

Plug value of M into (1)                             95 – 5  =  B + 5  

Combine like terms                                         85  =  B    

 

My Brother currently has 85 dollars   

 

check answer  

 

Plug 95 and 85 into (2)                            (95 + 25)  =  (2)(85 – 25)   

                                                                         120  =  2 • 60   

                                                                         120  =  120  

.

Jul 6, 2023