A puppy that was initially 8kg inceases its weight by 10% each month. how long does it take for the dog to be at least 3kg heavier than its original weight?

Question

give your answer as a whole number of months

Answer 1

Each month the previous weight is increased by 10%

or multiplied by a factor of 1.1

 

8(1.1)^m ≥ 11

 

Let's see how long it takes to reach 11 kg

 

1.1^m = 11/8

Take log of both sides

log 1.1^m = log (11/8)

m(log 1.1) = log (11/8)

m = [log(11/8)/log(1.1)]

m = 3.34 months

 

Since it takes more than 3 months,

round up.  In 4 months the puppy will

weigh more than 11 kg