Cost of 1 notebook is $ 1.85 and cost of 1 pen is $ 0.65
<h3><u>Solution:</u></h3>
Let "a" be the cost of 1 notebook
Let "b" be the cost of 1 pen
Given that John spent $10.65 on 4 notebooks and 5 pens
cost of 1 notebook x 4 + cost of 1 pen x 5 = 10.65
4a + 5b = 10.65 ------ eqn 1
Given that Ariana spent $7.50 on 3 notebooks and 3 pens
3a + 3b = 7.50 ----- eqn 2
Let us solve eqn 1 and eqn 2 to get the values of "a" and "b"
Multiply eqn 1 with 3
12a + 15b = 31.95 ---- eqn 3
Multiply eqn 2 with 4
12a + 12b = 30 ------ eqn 4
Subtract eqn 4 from eqn 3
12a + 15b = 31.95
12a + 12b = 30
(-) ---------------------
3b = 1.95
b = 0.65
Substitute b = 0.65 in eqn 1
4a + 5(0.65) = 10.65
4a = 7.4
a = 1.85
Thus cost of 1 notebook is $ 1.85 and cost of 1 pen is $ 0.65
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