just a clarification on a maths question.

[deltanova]

i have been given this question as part of a maths assignment so i dont want to be put into a situation where i might be advantaged against my other classmates with too much extra help but i was wondering if anyone could help me define y in this, im pretty confident that i have the right answer. i just cant think of the words to define it.

 

A motorist covered the first third of the distance at 60km/hr and the next third at 90km/hr. If the average speed for the whole trip was 80km/hr, what was the speed for the final third of the trip?

 

Here is my answer:

 

 

[math] \frac{y}{3} [/math] =80

y= 240

 

60+90+x=240

150+x=240

x=90

 

 

the speed for the last third of the trip was 90km/hr

 

i have tried to define y myself as the total of all speeds, can anyone offer a better clearer more precise one? cos im stuck

[Cloud]

Yeah - you're right.

 

There's nothing much more you can to do. The mean will always be inaccurate anyway so there isn't a clearer precise answer.

 

90 km/hr is correct.

[deltanova]

Ahhh so thats what y is, the mean? thanks loads cloud, i owe ya one only two questions left and my assignments finished

 

thanks loads

[Cloud]

No - the y isn't the mean

 

The mean (average) is 80 km/hr

 

y is just the constant that is needed in order to carry out a division of 3 to obtain the mean. Which you've done.

[deltanova]

oh oki doke, good to know i know what im doing hehe. (im amazed i got the answer right first time)