The amount invested in both the 9% and 12% account are :
Let :
Amount invested in 9% account = p
Amount invested in 12% account = 14000 - p
Total interest earned = 1350
Recall :
- Simple interest = Principal × rate × time
- Interest from 9% account + interest from 12% account = 1350
(p × 9% × 1) + ((1400 - p) × 12% × 1) = 1350
0.09p + 1680 - 0.12p = 1350
-0.03p = 1350 - 1680
-0.03p = - 330
p = 330 / 0.03
p = 11000
Hence,
Amount invested in 9% account = 11,000
Amount invested in 12% account = 14000 - 11000 = 3000
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1/2(12-v)=1/6(v-6)
6-1/2v=1/6v-1
7=2/3v
v=21/2 or 10.5
I believe it’s B. The others didn’t seem correct.
Let the number of hour it took them to have completed the same number of problems be x, then
15 + 10x = 9 + 12x
12x - 10x = 15 - 9
2x = 6
x = 6/2 = 3
After 3 hours, they must have completed the same number of homeworks.
