Correct Answer: C

Rationale: To find the sum of the digits of the number 72, you simply add the individual digits together: 7 + 2 = 9. Therefore, the sum of the digits is 9. Choice A (6), Choice B (5), and Choice D (7) are incorrect as they do not correctly sum up the individual digits of the number 72.

Correct Answer: C

Rationale: Let Lulu's sister's age be x. According to the given information, x = 15 (cousin's age) + 7 = 22. So, Lulu's sister is 22 years old. Since Lulu is 5 years younger than her sister, Lulu's age is 22 - 5 = 17. Therefore, Lulu is 17 years old. Choices A, B, and D are incorrect because they do not correspond to the calculations based on the information provided in the question.

Correct Answer: D

Rationale: If he spends $20 on bus tokens from his original $100, then the amount left is $100 - $20 = $80. The remaining 90% of $80 is calculated as $80 + 0.90 * $80 = $80 + $72 = $89.30. Therefore, the correct answer is $89.30. Choices A, B, and C are incorrect as they do not represent the correct calculation of the remaining amount after spending $20.

Correct Answer: D

Rationale: To find the product of 15 and 52, you simply multiply them together: 15 x 52 = 780. Therefore, the correct answer is 7.8. Choices A, B, and C are incorrect as they represent fractions or decimals much smaller than the correct product of 780.

Correct Answer: C

Rationale: Stu purchased 6 cups at 25 cents each, totaling $1.50 (6 cups x $0.25 = $1.50). He also bought 6 plates at 75 cents each, totaling $4.50 (6 plates x $0.75 = $4.50). Therefore, the total cost of the cups and plates is $1.50 + $4.50 = $6. Stu paid with a $10 bill, so the change he was owed is $10 - $6 = $4. Stu was owed $4 in change. The correct answer is $5, not $4 as he was owed that amount. Option A, $4, is incorrect as it miscalculates the change amount. Option B, $4.50, is incorrect as it does not consider the correct total cost. Option D, $5.50, is incorrect as it overestimates the change Stu was owed.