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# If x and y are postive integers with x + y < 40, what i the largest possible product xy?

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### 6 Answers

- 1 decade agoFavorite Answer
I'd say it would be 20*19, since x+y<40. Therefore if it was 20 and 20, then that would not be < 40.

- chess_is_bestLv 61 decade ago
As x gets closer to y, the product becomes larger. (ie. 38*1 = 38, 37*2 = 74, 36*3 = 108, etc). The largest possible sum is 39. Therefore the largest product would be 19*20 = 380

- somersetLv 44 years ago
x-y =11 so x = y +11 replace this in first equation xy = 80 (y+11)y = 80 y 2 +11y = 80 y 2 + 11 y - 80 = 0 fixing for y, y = -sixteen or 5 replace in 2d equation, x - y = 11 if y = -sixteen then, x +sixteen = 11 or x = -5 or if y = 5 then x -5 = 11 or x = sixteen so, there are 2 contraptions of solutions. ie x = sixteen and y = 5 or x = -5 and y = -sixteen

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- 1 decade ago
x = y = 20 would be the fulcrum point where x*y is the greatest. Therefore, the largest product is 20*20 = 400.