方程叻...請答

Let x be the number of type A
45x+80(7-x)=420
45x+560-80x=420
45x+560=420+80x
35x=140
x=4
Type A is 4,Type B is 3

Let x and y be the numbers of lipsticks A and B respectively.
Then , we have
x+y=7<------(1)
45x+80y=420<------(2)
From (1) , x+y=7
y=7-x<---------(3)
Sub (3) into (2),
45x+80(7-x) = 420
45x+560-80x=420
-35x=-140
x=4
When x=4 , y=7-4 = 3

Therefore , she had bought 4 lipsticks of type A and 3 lipsticls of type B.

Let the number of lipstick A be x,
then the number of lipstick B will be 7-x (as totally she bought 7 pcs of lipsticks)

45x + 80(7-x) = 420

($45 times x will be the total money spent on buying lipstick A,
$80 times (7-x) will be the total money spent on buying lipstick B, then altogether Mrs.
Lee spent $420)

45x + 560 - 80x = 420

560 - 420 = 80x - 45x

140 = 35x

x = 4

Therefore, the number of lipstick A is 4, the number of lipstick B is 4