i dont get it?

Question

ramos buys some pens and pencils . he buys 7 more pens then pencils . pens are 0.45 pencils are 0.40
he only has 10 to spend . how many of each can he buy

Answer 1

say he buys x pencils. then he buys x+7 pens.
he spends .4x + .45(x+7) = .85x=3.15
.85x + 3.15 <= 10
.85x <= 6.85
x = 8 (oviously the answer must be an integer, he can't buy 8.2 pens.

8 pencils $3.20
15 pens $6.75
spends $9.95

Answer 2

Let NumPen = number of pens
and NumPencil = number of pencils

We know that NumPen = NumPencil + 7

Cost of buying pens = cost per pen * number of pens
=> Cost of pen = 0.45*NumPen
Since NumPen = NumPencil + 7
We get: Cost of pen = 0.45*(NumPencil + 7)

By similar logic
Cost of pencils = 0.40*NumPencil

Total Cost = Cost of pen + cost of pencil
Since we know total cost is 10
We can write:
10 = 0.40*NumPencil + 0.45*(NumPencil + 7)
10 = 0.40*NumPencil + 0.45*NumPencil + 0.45*7
10 = 0.85*NumPencil + 3.15
6.85 = 0.85*NumPencil
NumPencil = 8.06, but since we can only buy whole numbers of pens, we will round it down to 8 pencils.
Since we can buy 8 pencils, that means we can buy 15 pens, since we need 7 more pens than pencils.

8 Pencils and 15 Pens

Answer 3

8 pencils and 15 pens

Answer 4

Let no. of pens = x at 0.45 each
Let no. of pencils = y at 0.40 each
x - y = 7
0.45 x + 0.4 y = 10
0.45 x + 0.4.(x - 7) = 10
0.85x - 2.8 = 10
0.85x = 12.8
x = 15 to nearest whole number. (Pencils)
y = 8 to nearest whole number.(Pens)