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作者: jilin1960 時間: 15-5-23 14:34 標題: 請教數學題

Justin wrote 6numbers.the average of first 4 numbers is 30 more than the average of the last 2 numbers.the sum of these numbers is 1770, if the fifth number is 186,what is the sixth number.

Thx.

作者: karen55407 時間: 15-5-23 16:36 標題: 回覆：jilin1960 的帖子

364

作者: 王家爸爸 時間: 15-5-23 16:48

jilin1960 發表於 15-5-23 14:34
Justin wrote 6numbers.the average of first 4 numbers is 30 more than the average of the last 2 numbe ...

Let the 6 numbers be A, B, C, D, E and F.
(A+B+C+D)/4 = (E+F)/2 + 30 ......................... (1)
(A+B+C+D)+(E+F)=1770    ......................... (2)
E=186  .................... .................... .................. (3)

(1) -> (A+B+C+D) = 2(E+F) + 120  .................(4)
Sub (4) into (2) -> 2(E+F) + 120 + (E+F) = 1770
   3(E+F) = 1650
   E+F=550
   F = 550 - E = 550 -186 = 364
Therefore, the sixth number is 364.

作者: momama 時間: 15-5-23 16:58 標題: 回覆：請教數學題

For which grade?

X is sum of first four numbers
Y is sum of last two numbers

X/4=Y/2 + 30
X+Y=1770

Y=550

Last number is 364

作者: momama 時間: 15-5-23 17:00 標題: 回覆：請教數學題

For which grade? X is sum of first four numbers, Y is sum of last two numbers, X/4=Y/2 + 30, X+Y=1770, Y=550, Last number is 364. 唔識隔行

作者: karen55407 時間: 15-5-23 17:02 標題: 回覆：王家爸爸的帖子

我不是用代數計。列式為（1770-30x4)/3-186=364

作者: jilin1960 時間: 15-5-23 19:17

Thx a lot!

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