The sample mean is approximately normally distributed with mean $75.00 and standard deviation $15.00/sqrt(64)
1) The z-score for $70.00 is
(70 - 75)/(15/8) = -2.66667 = -2.7 to the nearest tenth.
2) The probability corresponding to this z-score is 0.0035 (use standard normal tables), or 0.35%, which rounded to tenths is 0.4%
I will leave the rest to you. The instruction in step 5 is wrong; you do not add the probabilities from steps 1 and 3. (If you do add them, you will get 1, which is clearly the wrong answer.)
P(70 < sample mean < 80) = P(sample mean < 80) - P(sample mean < 70)
so you should subtract the result in step 1 from the result in step 3.
The correct answer is 0.993, or 99.3%
There are a couple of equations u can use
x = original price
15% off the original price of the purchase :
x - 0.15x
OR
if u get 15% off, then u are paying for 85%
0.85x
