請教數學題

jilin1960

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.

karen55407

364

王家爸爸

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.

momama

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

momama

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

karen55407

我不是用代數計。列式為（1770-30x4)/3-186=364

jilin1960

Thx a lot!