Last year, manuel saved $50 per month . this year, he increases his monthly savings by 25%. he plans to buy a smart phone for $375. at this rate, how long will it take him to save enough money to buy the smart phone if he starts saving for it this year?

From a normally distributed population,  if two samples of size less than 30 taken out , then we use t-test to test the difference between the population means.

The conditions which are necessary to use a t-test are :-

1. Each population must have normal distribution.

2. Both the samples must be independent.

Now, if a teacher is experimenting with a new computer-based instruction and conducts a study to test its effectiveness, then to use a t-test all the above conditions are necessary.