Thelmas average driving speed is 7 miles per hour faster than dougs in the same length of time it takes thelma to drive 174 miles doug only drives 153 miles whta is thelmas average driving speed?
2007-03-17 15:13:49 · 3 answers · asked by Anonymous in Education & Reference ➔ Homework Help
If Doug's average driving speed is the variable x
Then Thelma's driving speed is x + 7
Speed is Distance over Time
so to get the speed of Doug divide the Distance Doug travels by the time and then divide the distance Thelma travels by time.
Since the length of time is the same. We can set that as a variable t.
Therefore: Doug's speed is 153/t
and Thelma's speed is 174/t
We can set up 2 equations
x = 153/t and x+7 = 174/t
Two equations and two variables. We can solve this
Isolate t on both equations
t = 153/x and t = 174/x+7
Lastly, since the t variables are equal then
153/x = 174/x+7
Isolate and solve for x (use cross multiplication)
153(x+7) = 174x
153x + 1071 = 174x Subtract 153x from both sides
21x = 1071
x = 51
x is Doug's speed. Thelma's speed is 7 miles faster than Doug's speed.
Therefore Doug's speed is 58 mph.
2007-03-17 15:35:53 · answer #1 · answered by Michael784 2 · 0⤊ 0⤋
so, miles per hour, so divide 174 by 60 (for an hour) and you should get the average speed of thelma.
the long way is to take dougs speed, 153 divide by 60, then add 7 mph.
(both should be around the same speed)
2007-03-17 15:21:16 · answer #2 · answered by Catie 2 · 0⤊ 0⤋
s * t = 153
(s + 7) * t = 174
t = 153 / s
(s + 7) * (153 / s) = 174
153 + (1071 / s) = 174
1071 / s = 21
1071 = 21 * s
s = 51
(just for ghits and siggles, t = 3)
2007-03-17 15:25:28 · answer #3 · answered by Horsmn4 4 · 0⤊ 0⤋