Suppose Tina makes 15 ribbons every minute. How many ribbons did Tina make in an hour?

Answer 1

There are 60 minutes in a hour.

Tina makes 15 ribbons during the 1st minute

Tina makes 15 ribbons during the 2nd minute

Tina makes 15 ribbons during the 3rd minute

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Tina makes 15 ribbons during the 60th minute.

So Tina made 15+15 +15 +...+15 (60 times) = 15*60=900