Graphs and Relations Last Q

[99.96]

For the last question, (how long can they talk to each other on the radio)
What did everyone get?
I got 1.38 hours, but i dont think ill get the marks for it anyway cos i didnt indicate that it was the answer.

[AnonymousLover]

I got 2 hours?

[alpiano69]

1.375

[M2Char]

1.375

This. Rounded off to 2dp, 1.38.

[Haras_Etak]

i got 5.33 hours. I'm beginning to think this is wrong...

[Furbob]

how did you guys work it out? I just went through substituting when t=1 up until t=7 and just counted which hours within the 3km distance (which was 2 hours) but knowing that the question asked for 2 dp im pretty sure im wrong

[Haras_Etak]

I subtracted the girls equation from the other one and put it to equals less than 3. That meant t>5/3. Then i subtracted that from 7 but I think I just should have left it

[99.96]

i did distance of girl - distance of guy = 3
found t for that which was 1.625
3-1.625 = 1.375

[tea.squaredd]

I subtracted the girls equation from the other one and put it to equals less than 3. That meant t>5/3. Then i subtracted that from 7 but I think I just should have left it

That's what I did. However, i think we forget that one of the equations is only HALF the distance of the Guy. So some manipulation with the other half he travels is needed. Fml.

[M2Char]

how did you guys work it out? I just went through substituting when t=1 up until t=7 and just counted which hours within the 3km distance (which was 2 hours) but knowing that the question asked for 2 dp im pretty sure im wrong

Find the first boundary by making the girl's equation equal the equation of the first part of the guy's hike plus 3.
Solve for t.
t = 1.625

Find the second boundary by making the girl's equation equal the equation of the second part of the guy's hike minus 3.
Solve for t.
t = 3

The time between those boundaries is the time that they are within 3km of each other.

3 - 1.625 = 1.375 ~= 1.38 hours

[davidle_10]

An easier way to think about it is to actually draw the graph of d=16-3t on the same axis.

[xdecay]

i did distance of girl - distance of guy = 3
found t for that which was 1.625
3-1.625 = 1.375

sorry why did you have to minus 1.625 from 3?

[some dude]

i did distance of girl - distance of guy = 3
found t for that which was 1.625
3-1.625 = 1.375

sorry why did you have to minus 1.625 from 3?

because the walkie talkie was in range at 1.625 hours and went out of range after 3 hours. so total hours is 3-1.625 =1.38
its easier to understand when you look at the graph

[some dude]

I got 1.38 hours, but i dont think ill get the marks for it anyway cos i didnt indicate that it was the answer.

what do you mean indicate? as long as its the last number you write isnt that enough?