Janson bought 7 identical pens and had $4.20 left. He could have bought 10 pens with all his money. How much did Janson have?

Answer 1

$4.20 is 3/10 of what he had ... (10 - 7) / 10

$4.20 / .3 = ?

Answer 2

Let Y = cost of each pen
10Y = 7Y + 4.20
3Y = 4.20
Y = 1.40 = cost of each pen; therefore,
10 pens@ 1.40 each = $14.00 is how much money Ben had initially.