Let the principal amount be x
Amount invested at 4% = 0.04x
Amount invested at 5%, three times as much as the amount in = 3 (0.05x)
Total income from the two investments: 2,280
0.04x + 3(0.05x) = 2,280
0.04x + 0.15x = 2 280
0.19 x = 2 280
0.19 x = 2, 280
0.19 0.19
x = 12,000
Amount invested at 4% (x), is $12,000
Amount invested at 5%,
3x = 3 ×12,000 = $ 36,000
To check the interest earned:
at 4% = 0.04 × 12,000 = $ 480
at 5% = 0.05 × 36,000 = $ 1,800
Add the interest: 480 + 180 = 2,280