Answer:
It takes at least 7 months for the cat to be at least 6 kg lighter than the original weight.
Explanation:
Use exponential decay formula:
A = P (1-r)t
A = amount decreased to
P = original amount
r = rate of decrease
t = time
6 ≥ 12 (1-0.10)t divide both sides by 12
0.5 ≥ (0.9)t take log of both sides
log (0.5) ≥ log (0.9)t power rule of logs lets the exponent t drop to front of log to become a factor
log (0.5) ≥ t log(0.9) divide both sides by log(0.9) which is negative so reverse the inequality sign
log (0.5) / log (0.9) ≤ t use calculator
6.57 ≤ t
It takes at least 7 months for the cat to be at least 6 kg lighter that original weight.
check:
12 (0.9)7≈ 5.73
12 (0.9)6 ≈ 6.37