# Thread: have i got the units right in this calculation?

1. Hi all. I have been given the following and am not confident i have got the units correct so was hoping someone could help me.

d.The equation for a straight line is often used in science to find an unknown without reference to a graph. For a set of data for two quatities, A and B, where A is plotted on the x-axis and B on the y-axis, the gradient of the straight line is 2.3 × 104m s−1 and the intercept on the y-axis is 5.8 × 104 m. Using the equation for a straight line (Book 3, Equation 7.12 ) as your starting point, determine the value for A when B = 6.2 × 105 m. Show all your workings and give your answer in scientific notation and to two significant figures.
Y =mx + c

C = 5.8 × 104 m
M= 2.3 × 104m s−1
B = 6.2 × 105 m

6.2 × 105 m 2.3 × 104m s−1 A 5.8 × 104 m
6.2 × 105 m - 5.8 × 104 m = 2.3 × 104m s−1 A
620000m – 58000 m s−1= 23000 m A
562000 s = 23000m A
562000s = A
23000m
24.434782608695652173913043478261s = A
A = 24s to 2 significant figures.

2.

3. Originally Posted by studley89
Hi all. I have been given the following and am not confident i have got the units correct so was hoping someone could help me.

d.The equation for a straight line is often used in science to find an unknown without reference to a graph. For a set of data for two quatities, A and B, where A is plotted on the x-axis and B on the y-axis, the gradient of the straight line is 2.3 × 104m s−1 and the intercept on the y-axis is 5.8 × 104 m. Using the equation for a straight line (Book 3, Equation 7.12 ) as your starting point, determine the value for A when B = 6.2 × 105 m. Show all your workings and give your answer in scientific notation and to two significant figures.
Y =mx + c

C = 5.8 × 104 m
M= 2.3 × 104m s−1
B = 6.2 × 105 m

6.2 × 105 m 2.3 × 104m s−1 A 5.8 × 104 m
6.2 × 105 m - 5.8 × 104 m = 2.3 × 104m s−1 A
620000m – 58000 m s−1= 23000 m A
562000 s = 23000m A
562000s = A
23000m
24.434782608695652173913043478261s = A
A = 24s to 2 significant figures.
The problem is much simpler than what you made out. The question is: when Y = B, what is X (=A)?

4. Thank you, i'm still finding it pretty confusing so your feedback is much appreciated!

5. Originally Posted by studley89
Thank you, i'm still finding it pretty confusing so your feedback is much appreciated!
The original statement is y = mx + c, so elementary algebra gives x = (y-c)/m.

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