If Peter's age is currently half of his mother's age, who is 60, Peter is 1 / 2 * 60 = 30 years old. In four years, Peter will be 30 + 4 = 34 years old. Since Peter's age in four years will be twice Harriet's age, Harriet will be 34 / 2 = 17 years old in four years. Currently, Harriet is 17 - 4 = 13 years old.
The answer: 13
Reverse engineering the question: In four years, Peter will be twice as old as Harriet. If Peter's age is currently half of his mother's age, who is 60, how old is Harriet now?

At a rate of 30 minutes per poodle, 3 poodles will take 3 * 30 = 90 minutes. If it takes half as much time to groom a terrier as it takes to groom a poodle, it takes 30 / 2 = 15 minutes per terrier. At a rate of 15 minutes per terrier, 8 terriers will take 120 minutes. Thus, in total, it will take the pet shop 90 + 120 = 210 minutes to groom 3 poodles and 8 terriers.
The answer: 210
Reverse engineering the question: The pet shop grooms dogs. It takes 30 minutes to groom a poodle. It takes half as much time to groom a terrier as it takes to groom a poodle. They do not groom cats. If the pet shop grooms 3 poodles and 8 terriers, what is the total length of time it will take, in minutes?

If John gave his fiancee a $4000 ring on their engagement day, a $2000 car as a gift on their wedding day, the total cost for the two presents is $4000 + $2000 = $6000. He also gave his fiancee a diamond brace twice as expensive as the ring costing 2 * $4000 = $8000. The total worth of the presents John gave to his fiancee is $6000 + $8000 = $14000.
The answer: 14000
Reverse engineering the question: John gave his fiancee a $4000 ring on their engagement day, a $2000 car as a gift on their wedding day, and a diamond brace twice as expensive as the ring he gave her during the engagement. What's the worth of the presents John gave to her fiancee?

Janeth bought 5 x 20 = 100 round balloons. She bought 4 x 30 = 120 long balloons. So, she has a total of 100 + 120 = 220 balloons. Since 5 round balloons burst, then there are only 220 - 5 = 215 balloons left.
The answer: 215
Reverse engineering the question:
Janeth bought 5 bags of round balloons with 20 balloons in each bag. She also bought 4 bags of long balloons with 30 balloons in each bag. While blowing up the balloons, 5 round balloons burst. How many balloons are left?