# ECAA November 2020 help

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#1
Hi, I'm preparing for Cambridge Econ for 2022 entry, and I'm stuck on an ECAA question from November 2020.

The number of pairs of winter boots sold on a day is inversely proportional to the cube of the outside temperature on that day, measured in degrees celsius.

On a day when the outside temperature is 8 degrees celsius, 250 pairs of boots are sold.

The next day, when the outside temperature is x degrees celsius, the number of pairs of boots sold is 700% more than on the previous day.

What is the value of x?

A) 2
B) 4
C) 8/cube root 7
D) 8 cube root 7
E) 16
0
1 month ago
#2
Number of pairs of boots sold = k/(Temp. in degrees celsius)^3
250 = k/8^3
Hence, k = 128000

Pairs of boots sold the next day: 1750 + 250 = 2000
Ergo, for next day:
2000 = 128000/x^3
x^3 = 64
x = 4

1
#3
(Original post by eBoD31415)
Number of pairs of boots sold = k/(Temp. in degrees celsius)^3
250 = k/8^3
Hence, k = 128000

Pairs of boots sold the next day: 1750 + 250 = 2000
Ergo, for next day:
2000 = 128000/x^3
x^3 = 64
x = 4

Great, thank you so much!
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