Proportionality and percentages

# Banking interest

The profit that we obtain when we lend our money is called **interest**. This profit is directly proportional to the **time** that the loan lasts and to the **amount** that we lent. The percentage of profit is called **interest rate**. Then we have a compound rule of three:

Example 1: A bank offers an interest rate of 4%. What interest will we obtain if we deposit 750€ for 3 years?

We obtain 90 €

Example 2: How much money will I have to pay back to the bank if it lends me 2000€ at 5% for 4 years?

I'll have to pay back 2400 €

**Exercises**:

1.- What interest will I obtain if we deposit 1500 € for 10 years at 3%?

2.- How much money will I have to deposit in a bank for 5 years at 5% to obtain 5000€ of interest?

Solutions: 1) 450 €; 2) 20000 €

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