Set up a proportion.
= 
Cross multiply.
2x=36
x=12
It would take her 12 minutes.
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Formula for surface area of a cube: 6a² where a=20.
6 x (20)²
6 x 400
= 2400
Surface area: 2400 cm
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Mean absolute deviation: The average distance from each number in the set to the mean of the set.
Mean of the set:
9.6-3=6.6
9.6-8=1.6
10-9.6=0.4
12-9.6=11.4
15-9.6=5.4
Mean of 6.6, 1.6, 0.4, 11.4, and 5.4:
Cross multiply.
2x=36
x=12
It would take her 12 minutes.
-----------------------------------------
Formula for surface area of a cube: 6a² where a=20.
6 x (20)²
6 x 400
= 2400
Surface area: 2400 cm
----------------------------------------------
Mean absolute deviation: The average distance from each number in the set to the mean of the set.
Mean of the set:
9.6-3=6.6
9.6-8=1.6
10-9.6=0.4
12-9.6=11.4
15-9.6=5.4
Mean of 6.6, 1.6, 0.4, 11.4, and 5.4: