We will give solution of the following problem:

"Dag's invested part of 4000 pesos at 5% and the remainder at 3% simple interest. The total income per year from the investment is 168 pesos , how much did he invest at each rate. Solve for x"

Let 'x' the money invested at 5% then the rest of the money, 4000 - x, is invested at 3% simple interest.

The total interest earned per year is 168 pesos means:

0.05x + 0.03(4000 - x) = 168

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click here to see the equation solved for x

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x = 2,400 pesos

4,000 - 2,400 = 1,600 pesos

Dag invested 2,400 pesos at 5% and 1,600 pesos at 3%.