Difference between revisions of "2020 AMC 10A Problems/Problem 10"
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The volume of each cube follows the pattern of <math>n^3</math> ascending, for <math>n</math> is between <math>1</math> and <math>7</math>. | The volume of each cube follows the pattern of <math>n^3</math> ascending, for <math>n</math> is between <math>1</math> and <math>7</math>. | ||
| − | We see that the total surface area can be comprised of three parts: the sides of the cubes, the tops of the cubes, and the bottom of the <math>7\times 7\times 7</math> cube (which is just <math>7 \times 7 = 49</math>). The sides areas can be measured as the sum <math>4\sum_{n=0}^{7} n^2</math>, giving us <math> | + | We see that the total surface area can be comprised of three parts: the sides of the cubes, the tops of the cubes, and the bottom of the <math>7\times 7\times 7</math> cube (which is just <math>7 \times 7 = 49</math>). The sides areas can be measured as the sum <math>4\sum_{n=0}^{7} n^2</math>, giving us <math>560</math>. Structurally, if we examine the tower from the top, we see that it really just forms a <math>7\times 7</math> square of area <math>49</math>. Therefore, we can say that the total surface area is <math>560 + 49 + 49 = \boxed{\textbf{(B) }658}</math>. ~ciceronii |
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| + | Alternatively, for the area of the tops, we could have found the sum <math>\sum_{n=0}^{6}((n+1)^{2}-n^{2})</math>, giving us <math>49</math> as well. | ||
==See Also== | ==See Also== | ||
Revision as of 21:51, 31 January 2020
- The following problem is from both the 2020 AMC 12A #7 and 2020 AMC 10A #10, so both problems redirect to this page.
Problem 10
Seven cubes, whose volumes are 
, 
, 
, 
, 
, 
, and 
cubic units, are stacked vertically to form a tower in which the volumes of the cubes decrease from bottom to top. Except for the bottom cube, the bottom face of each cube lies completely on top of the cube below it. What is the total surface area of the tower (including the bottom) in square units?
Solution
The volume of each cube follows the pattern of 
ascending, for 
is between and 
.
We see that the total surface area can be comprised of three parts: the sides of the cubes, the tops of the cubes, and the bottom of the 
cube (which is just 
). The sides areas can be measured as the sum 
, giving us 
. Structurally, if we examine the tower from the top, we see that it really just forms a 
square of area 
. Therefore, we can say that the total surface area is 
. ~ciceronii
Alternatively, for the area of the tops, we could have found the sum 
, giving us as well.
See Also
| 2020 AMC 10A (Problems • Answer Key • Resources) | ||
| Preceded by Problem 9 |
Followed by Problem 11 | |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | ||
| All AMC 10 Problems and Solutions | ||
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. 
