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Old 07-24-2007   #1
♥Starbucks
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Default i need some math help for this boy that i'm babysitting right now...?

it would be helpful if you could give me step by step directions into solving the problems. 1.Christina drove for six hours at an average speed of 45 mph. She drove 53 mph during the first two hours of her trip. How fast did she drive during the last four hours?2. Jonathan drove to the beach which is one hundred eighteen kilometers away, at sixty kph. He drove home the next day at seventy two kph. How many hours in total did Jonathan drive?3. Destiny drove to Jordan's house at 51 mph. Jordan's house is thirty nine miles away. Destiny arived at jordan's house at 2:58pm. What time did she leave?
 
Old 07-24-2007   #2
andrew k
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1. 41 mph(6(45)-2(53))/4 = 412. 3.6 hours(118/60) + (188/72) = 3.63. 2:12 PM(39/51)*60 = 462:58 PM - 46 minutes = 2:12 PMTedo: For question #2 she said 118 not 108
 
Old 07-24-2007   #3
Tedo
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Question #1:45mph x 6 hrs = 270 miles (total distance travelled)53mph x 2 hrs = 106 miles (distance in first 2 hours)270 miles - 106 miles = 164 miles (distance in last 4 hours)164 miles / 4 hours = 41 mphQuestion #2:Trip there: 108 km / 60 kph = 1.8 hrs = 1 hr 48 minTrip back: 108 km / 72kph = 1.5 hrs = 1 hr 30 minTotal time: 1.8 hrs + 1.5 hrs = 3.3 hrs = 3 hrs 18 minQuestion #3:39 miles / 51mph = 0.7647 hrs (rounded) = 45.882 minutesEnding time was 2:58pm so she left 45.882 minutes earlier or about 2:12pm.
 
Old 07-24-2007   #4
Katie I
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1. To find an average, you have to add all the separate units and divide by the total number of units. In this case, 45 mph (the average) is equal to the sum of how fast she drove each hour divided by 6. So, 6*45 = 270, and therefore 270 = the sum of how fast she drove each hour. If she drove 53 mph for the first 2 hours, you can subtract 106 from 270 = 164. Therefore, to find the average of how fast she drove for the last 4 hours, divide 164/4 = 41. 41mph is the answer.2. distance = rate*time. Therefore, distance/rate = time. 118/60 = 1.9666 hours going there118/72 = 1.6388 hours coming backAdd the two to find the total hours. He drove a total of 3.6 hours.3. Use the same equation from above. Distance = rate*time. You distance, you know rate, so you can find out how much time it took and then subtract that from the arrival time.39/51 = .765 hour = 45.88 minutes2:58 - 45.88 = 2:12pm
 
Old 07-24-2007   #5
casolari21
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1. 53+x/2= 45answer: 372. 180/x=72/1 ------> 3 hours 180/x=72/1 ------->2.5 hoursanswer: 5.5 hours3. 2:13
 
Old 07-24-2007   #6
VIJAY
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1. 45*6 = 270 miles total53*2 = 106 miles in first two hours270-106 = 164 miles in next 4 hoursat average speed of 164/4 = 41mph in next four hours2.118/60 = 1.967 hours one way118/72 = 1.638 hours on returnTotal 3 hours & 36+ minutes3.39/51 = 0.765 hours which is 46 minutes ..2:12 PM she left the house
 
Old 07-24-2007   #7
Lui
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1. let s 45=[ ( 53 x 2 )+( s x 4 ) ] / 6 45x6 = 106 + 4s 270-106=4s 164=4s s=41mphso the speed for the last 4 hours is 41 mph2.drove to the beach= 118/60=1h 58 min drove back to home= 118/72 = 1 h 38 min Total time taken = 3 hours 36 minutes3. time taken = 51/39 = 46 min 2.58- 0.46= 2.12pm
 
Old 07-24-2007   #8
037 G
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Part 1. Here you have to combine using logic, common sense, and a little math you will get: if you drive 45 for six hours you have gone 45x6= 270 miles. So your total trip is 270 miles long.Now if you drive for 2 hrs at 53 mph you will have completed the first 106 miles (53x2) of the same 270 mile trip leaving 164 miles to be driven to complete this trip (270-106=164)Next the question becomes how fast do you have to drive to complete a 164 mile trip in 4 hrs (164/4=41) so you would have to drive 41mph to complete the remaining 164 miles in 4 hrs after doing the first 106 miles in 2 hrs at 53 mph. hope this helps for the first question.Part 2. Jonathan spent 1.9667hrs driving to the beach on the first day (118/60= 1.9667, I suspect you have a typo and ment to say 180km in which case the answer is 3hrs from 180/60) anyway, the next day he drives 1.638 hrs from (118/72 = 1.638 with the typo it is 180/72= 2.5 hrs) either way you add the hrs from both days to get the total. 1.9667+1.638=3.6047 hrs but I think it is more likely to be 3+2.5=5.5 hrs if the beach were 180 km away.Part 3. Destiny drove 39mi at 51mph so she drove for 0.764 hrs(time= distance/ speed = 39/51= 0.764 hrs), Now .764 hrs is approximately 46 minutes (.764x60=45.8823) so 46 minutes before 2:58 PM the time was 2:12 PM that is when she left.
 
 

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