Roberto invested a total of $1,part at 6% and part at 9%. how much did he invest in the higher interest account if the total interest earned in one year was $810?

Step-by-step explanation:

Let x represent the amount invested at 9%. Then Roberto's interest was ...

  x(9%) +(10000-x)(6%) = 810

  0.03x + 600 = 810 . . . . . . . . . simplify

  0.03x = 210 . . . . . . . . . . . . . . . subtract 600

  x = 210/0.03 = 7000 . . . . . . . divide by the coefficient of x

Roberto invested $7000 at the higher interest rate.

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