Answer:
-13
Step-by-step explanation:
it must be either -11 or -13. -13 is less than -12.
Answer:
b. Kathy
Step-by-step explanation:
We compare each of their score by how far away from the mean when in term of the standard deviation. Using the following formula

For John he is (85 - 75)/5 = 2.
For Kathy she is (80 - 50)/10 = 3.
Since Kathy is 3 standard deviation better than her class' average, while John is only 2's. We conclude that Kathy did better.
After 12 months, Quynh will have saved $800
Simply follow the pattern shown on the graph.
Month 1: 250
Month 2: 300
Month 3: 350
Month 4: 400
Month 5: 450
Month 6: 500
Month 7: 550
Month 8: 600
Month 9: 650
Month 10: 700
Month 11: 750
Month 12: 800