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Need help in two questions

Jury drives at an average speed of 80km per hour 2 hours and 45 minutes

Work out the number of miles judy drives

And.

Find an equation of the straight line that is perpendicular to the straight line x + 2y = 5 and that passes through the point (3, 7).

Reply 2

Lay-Z

80 x 2.75 = kilometers travelled then convert it to miles using a conversion

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Reply 3

Lay-Z

X+2y=5 so 2y=-x+5 so y=-x/2+5/2
For perpendicular product of gradients equals minus 1 therefore new line will have gradient 2 as 2 times -1/2 =-1. You can use formula y-y1=m(x-x1) now y-7=2(x-3)
Y-7=2x-6
Y=2x+1

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(edited 11 years ago)

Reply 4

Mihawk Gallio

Original post by Lay-Z

80 x 2.75 = kilometers travelled then convert it to miles using a conversion

Posted from TSR Mobile

How did you get 2.75

Thanks

Reply 5

Lay-Z

Original post by Mihawk Gallio

How did you get 2.75

Thanks

Distance = speed x time

2hrs 45 minutes is 2.75 hours as there are 60 minutes in a hour, 45/60 =0.75

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Reply 6

lilixxx1000

Original post by Mihawk Gallio

How did you get 2.75

Thanks

You said 2 hours and 45 mins. 45 mins is 75% of an hour because 45/60 = 75/100.

So in terms of decimals, 2 h 45 mins is 2.75 hours

Reply 7

Mihawk Gallio

Original post by lilixxx1000

You said 2 hours and 45 mins. 45 mins is 75% of an hour because 45/60 = 75/100.

So in terms of decimals, 2 h 45 mins is 2.75 hours

But how did you lot get 200?

In 1 hour there Is 60 mins so

60 x 2 = 120

So how did you get it to 200

(edited 11 years ago)

Reply 8

Mihawk Gallio

And how can I convert them without using a calculator

Reply 9

lilixxx1000

Original post by Mihawk Gallio

But how did you lot get 200?

In 1 hour there Is 60 mins so

60 x 2 = 120

So how did you get it to 200

I don't really know what you mean by the 200.

It's 2 hours and 45 mins, so you know that in terms of hours it'll be somewhere between 2 and 3. because 45 mins is 3/4 of an hour, it's 2.75.

to convert it on your calculator you do 45 / 60 = 0.75 and then multiply by 100 to get it as a percentage.

hope that helps and tell me if you don't understand i'll try to explain better.

Reply 10

Mihawk Gallio

I really don't get perpendicular lines.

The part I get stuck In is I changed x+2y=5

Into y= 1/2x+5 = 2.5

What next? D:

And now I get the other question thank you very much,

Reply 11

Lay-Z

=2.5=2.5x+2y=5, minus x to otherside to give 2y=-x+5 divide by two to get y=-1/2x

this is the equation of the same line y=-1/2x+2.5 is the same as x+2y=5

now you want the line thats perpendicular. The rule is the the product of the gradients of perpendicular lines always equals minus 1.

The gradient of the line is the co-efficent of x when the line is in the form y=mc+c, which it currently is therefore the gradient is -1/2 or -0.5

-0.5 x a number (Y) = -1 using the rule so Y = -1/-0.5 = 2

this tells you that the gradient of the line that is perpendicular to your line is 2

now you know the gradient you use the formula, y-y1=m(x-x1) where y1 is the given y co-ordinate m the gradient and x1 the given x co-ordinate (you can also use the formula they provide at gcse level, but i'd get used to this one)

y-7=2(x-3)
y-7=2x-6
y=2x+1 is the final answer

Reply 12

Mihawk Gallio

=2.5=2.5x+2y=5, minus x to otherside to give 2y=-x+5 divide by two to get y=-1/2x

I don't get this part

now you know the gradient you use the formula, y-y1=m(x-x1) where y1 is the given y co-ordinate m the gradient and x1 the given x co-ordinate (you can also use the formula they provide at gcse level, but i'd get used to this one)