Monoxdifly
Last Activity: 6 Years ago
If pens = x and pencils = y
Pack I = 3x + 5y
Pack II = 4x + 3y
Suppose the number of Pack I is a and the number of Pack II is b:
(3x + 5y)a + (4x + 3y)b = 18x + 19y
3ax + 5ay + 4bx + 3by = 18x + 19y
(3a + 4b)x + (5a + 3b)y = 18x + 19y
Look at the coefficients of x and y in both sides, we get:
3a + 4b = 18 … (i)
5a + 3b = 19 … (ii)
Multiply the equation (i) with 3 and the equation (ii) with 4:
9a + 12b = 54
20a + 12 b = 76
------------------------ –
-11a = -22
a = 2
Substitute a = 2 to the equation (i):
3a + 4b = 18
3(2) + 4b = 18
6 + 4b = 18
4b = 12
b = 3
So, we need to buy 4 packs of Pack I and 3 packs of Pack II.