Math Q destroyer e8 q2

[crax]

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Question:
Bob and Ray set off in opposite direction from the post office. Bob travels 10 mph faster than Ray. After 6 hours they are 540 miles apart. What is bob's speed?

(As a sidenote, would you mind showing your work in terms of Ray's speed?
(i.e. B= R+10)
Im not sure, but am i mistaken to assume B= R+10 ?

 

[rockclock]

Question:
Bob and Ray set off in opposite direction from the post office. Bob travels 10 mph faster than Ray. After 6 hours they are 540 miles apart. What is bob's speed?

(As a sidenote, would you mind showing your work in terms of Ray's speed?
(i.e. B= R+10)
Im not sure, but am i mistaken to assume B= R+10 ?

In 6 hours, Bob travels 6B and Ray travels 6R. Since they're moving in opposite directions, the distance between them is the sum of those: 6B + 6R = 540.

Substituting B = R + 10:

6(R+10) + 6R = 540
12R + 60 = 540
12R = 480
R = 40

And B = R + 10 = 50.

...or if you just wanted to do this in your head...540 miles/6 hours is 90 mph. Splitting that 90 up so that one is 10 more than the other is obviously 40 mph and 50 mph.

 

[crax]

thanks, for some reason when i did 540-60 in my head i ended up with 380. thanks :-/

 

[csulapredental]

In 6 hours, Bob travels 6B and Ray travels 6R. Since they're moving in opposite directions, the distance between them is the sum of those: 6B + 6R = 540.

Substituting B = R + 10:

6(R+10) + 6R = 540
12R + 60 = 540
12R = 480
R = 40

And B = R + 10 = 50.

...or if you just wanted to do this in your head...540 miles/6 hours is 90 mph. Splitting that 90 up so that one is 10 more than the other is obviously 40 mph and 50 mph.

if there moving opposite to one another how is the SUM there distance between

 

[DMikes]

if there moving opposite to one another how is the SUM there distance between

This is from 2011. These individuals will not reply.

However, to answer your question, if they're moving in opposite direction the distance between them is growing as they both move, thus, the distances are summed. If it were subtracted, you're implying they're moving closer to one another/in the same direction (depending which way)... And the problem would not work nor make sense.
6B - 6R = 540
B=R + 10
6(R+10) - 6R = 540
60 = 540
?

6 hours x 10mph difference = 60 miles not 540 miles