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Percentage change

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
What have you been thinking? Have you tried anything?
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
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
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
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%
Original post by MathMoFarah
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%

Hello, the correct answer is 49%. However, I'm also getting 51% as my answer. I don't know where the mistake is... Can you please share the correct solution?
Original post by paawanjot.kaur
Hello, the correct answer is 49%. However, I'm also getting 51% as my answer. I don't know where the mistake is... Can you please share the correct solution?

This post is five years old, so you will be very lucky to get a response from the original participants. However, I'll give you a couple of thoughts to consider.

1) If P had decreased to 0.99P, would you call that a 99% decrease, or would you call it something else?

2) In this question, P has decreased to 0.51P. Would you call that a 51% decrease? Apply the same thinking as in (1) and suggest what the % decrease her actually is.
Original post by old_engineer
This post is five years old, so you will be very lucky to get a response from the original participants. However, I'll give you a couple of thoughts to consider.

1) If P had decreased to 0.99P, would you call that a 99% decrease, or would you call it something else?

2) In this question, P has decreased to 0.51P. Would you call that a 51% decrease? Apply the same thinking as in (1) and suggest what the % decrease her actually is.

Really healpful. Thanks🤗👏

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