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# Percentage change Watch

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1. Two variables are connected by the relation: P
2
1
Q

Q is increased by 40%.
To the nearest percent, describe the change in P in percentage terms.
A 29% decrease
B 44% decrease
C 49% decrease
D 51% decrease
E 80% decrease
F 96% decrease
2. What have you been thinking? Have you tried anything?
3. (Original post by MathMoFarah)
What have you been thinking? Have you tried anything?
The question basically says P is inversely proportional to the square of q. If q has increased by 40%, whats the percentage change of P
4. (Original post by Hamza Rashid)
The question basically says P is inversely proportional to the square of q. If q has increased by 40%, whats the percentage change of P
The general policy on TSR is we don't answer the question until we see some evidence that you've attempted it - and even then we just try to point you in the right direction
5. (Original post by MathMoFarah)
The general policy on TSR is we don't answer the question until we see some evidence that you've attempted it - and even then we just try to point you in the right direction
Well what i initially tried to do was to just plug in the 40% into the equation but I put it in as 1.4 as it is a 40% increase. However, after doing the math, my answer was not the right one and I have no idea how else to approach the question
6. P is inversely proportional to Q^2
P is proportional to Q^-2
P=kQ^-2
Q has increased by 40% therefore Q becomes 1.4Q

P now represents a different value

P=kQ^-2(1.4)^-2
(1.4)^2P=kQ^-2
1.96P=kQ^-2

Therefore P has decreased by a factor of 1/1.4^2 or 1/1.96= 100/196=25/49 roughly equal to 51%

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Updated: September 25, 2016
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