Starting from the point (0,0), a grasshopper makes a series of moves on the coordinate plane. The grasshopper's first move takes her to (3,4). She then proceeds via this rule:

Move Rule: After a move which adds (x,y) to the grasshopper's coordinates, her next move adds either (x,y-1) or (x-1,y) to her coordinates.

Thus, her second move adds either (3,3) or (2,4) to her position, landing her at (6,7) or (5,8) accordingly.

If the grasshopper's x and y coordinates never decrease, and if she ends at the point (a,a) where a is as large as possible, then what is the value of a?

Could I have an explanation with the answer too? Thanks!!

User Icon for Steve Steve answered
7 years ago

since the coordinates never decrease, and she started by adding (3,4), she can only make 3 more moves which decrease the x amount added, making her maximum x value 3+2+1+0 = 6

Similarly for y, which can add a max of 4+3+2+1+0 = 10

So, she has to end up at (6,6)

User Icon for Tan. Os Tan. Os answered
5 years ago

14

User Icon for AoPS Admin AoPS Admin answered
4 years ago

Students...why do you cheat so much?

User Icon for 1232312213 1232312213 answered
4 years ago

its 14

User Icon for 1232312213 1232312213 answered
4 years ago

Here, we use a bit of imagination and let $s$ stand for the sum of the $x$ and $y$ coordinates of the grasshopper's current location.

Initially, $s = 0$. After the first move, the grasshopper is at $(3,4)$, so $s = 7$. The next move adds either $(3,3)$ or $(2,4)$. In either case, $s$ must increase by $6$, up to $13$. In the next moves, $s$ must increase by $5$, then $4$, then $3$, then $2$, then $1$. Finally, the grasshopper stops because she cannot continue moving without decreasing at least one of her coordinates.

After these moves, $s$ is equal to $7 + 6 + 5 + 4 + 3 + 2 + 1 = 28$. Since the trip ends at the point $(a,a)$, we have $28= s = 2a$. Therefore, $a = \boxed{14}$.

Notice that it is possible to get to $(14,14)$ by following the path: $(0,0)\rightarrow (3,4) \rightarrow (6,7) \rightarrow (9,9) \rightarrow (11,11) \rightarrow (13,12) \rightarrow (14,13) \rightarrow (14,14)$.

User Icon for 1232312213 1232312213 answered
4 years ago

from AOPS website

User Icon for yeyejuiceboy yeyejuiceboy answered
4 years ago

14

User Icon for Hithere Hithere answered
4 years ago

14 is the answer

User Icon for AoPS Admin AoPS Admin answered
3 years ago

At the bottom of the page it says "Copyright © AoPS Incorporated. This page is copyrighted material. You can view and print this page for your own use, but you cannot share the contents of this page with others."

Asking this question is against the rules and the law itself. Pls stop cheating

User Icon for hi! hi! answered
2 years ago

The answer is 14.

User Icon for D D answered
11 months ago

What grade are you in?