Answer:
$ 0.75 for one pen
$1.05 per notebook
Explanation:
John and Ariana bought school supplies. John spent $10.30 on 5 notebooks and 7 pens. Ariana spent $7.20 on 4 notebooks and 4 pens. What is the cost of 1 notebook and what is the cost of 1 pen?
John: 5n + 7p = 10.5
let's solve for n:
5n + 7p = 10.5
subtract 7p from both sides:
5n + 7p -7p = 10.5 - 7p
5n = 10.5 - 7p
divide both sides by 5:
5n/5 = (10.5 - 7p)/5
n = 2.1 - 7/5 p
Ariana: 4n + 4p = 7.20
Let's substitute in: n = 2.1 - 7/5 p
4n + 4p = 7.20
4(2.1 - 7/5p) + 4p = 7.20
multiply left side:
8.4 - 5.6p + 4p = 7.2
subtract 8.4 from both sides:
8.4 - 5.6p + 4p - 8.4 = 7.2 - 8.4
- 5.6p + 4p = -1.2
combine p terms on left side:
-1.6p = -1.2
divide both sides by -1.6:
-1.6p/(-1.6) = -1.2/(-1.6)
p = 0.75 cents for one pen
Now solve to find the price of a notebook:
4n + 4p = 7.20 when p = 0.75
4n + 4(0.75) = 7.20
4n + 3 = 7.20
subtract 3 from both sides:
4n + 3 - 3 = 7.20 - 3
4n = 4.2
divide both sides by 4:
4n/4 = 4.2/4
n = 1.05 per notebook
CHECK: when n = 1,05 and p = 0.75
John: 5n + 7p = 10.5
5(1.05) + 7(0.75) = 10.5
10.5 = 10.5
Ariana: 4n + 4p = 7.20
4n + 4p = 7.20
4(1.05) + 4(0.75) = 7.20
7.2 = 7.2
Answer assumes no additional sales tax.