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Sagot :
Answer:
Step-by-step explanation:
Train A is northbound at S km/hr S = speed and travels for 3 hours
S is the speed of Train A
Train B is southbound at (S + 20) km/hr
Train B starts later 45 min and travels for 2 and 1/4 hours so 3/4 hour plus 2 1/4 hour equals 3 hours
After 3 hours since Train A left the station Train A and Train B are 360 km apart
A + B = 360 km Equation 1
A = S km/hr x 3 hr
B = (S +20) km/hr x (2 1/4) hr
Plug A and B into the first equation
3S (km/hr) + (2 1/4)(S + 20) (km/hr)= 360 km
3S + (9/4)(S + 20) = 360 i dropped the units to make easier to read
3S + 9S/4 + 180S/4 = 360 I just multiplied 9/4 time the S +20
12S + 9S + 180 = 1440 multiply both sides by 4
12S + 9S = 1440 - 180 subtract 180 from both sides
21S = 1260 collecting terms
S = 60 km/hr S = Speed of Train A equal 60 km/hr I added the units back into the answer
S + 20 is the speed of
Train B = 80 km/hr
Extra credit
now using the same train speeds, if Train B was now headed NORTH, a what time would it crash into Train A?
S km/hr x T hr = (S+20) km/hr x (T-3/4) hr solve for T T = time in hr
When is Train A equal the same location as Train B
Trani A = Train B don't forget the start time differential
ST = (S + 20)(T-3/4) plug in train a and b speeds
60T = 80(T-3/4)
60T = 80T - 60
60 = 80T - 60T
60 = 20T
3 = T
after 3 hrs Train B will catch Train A
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