Answer:
- 10 2/3 years or 10 years and 8 months
Step-by-step explanation:
Assumed it is a simple interest with rate r.
Find the rate:
- 4000(1 + 8r) = 5000
- 1 + 8r = 5000/4000
- 8r = 1/4
- r = 1/32
Find the time for the second amount:
- 2100(1 + 1/32t) = 2800
- 1 + 1/32t = 2800/2100
- 1 + 1/32t = 1 1/3
- 1/32t = 1/3
- t = 32/3
- t = 10 2/3
