30 x 2 / 5 = 12 members ordered lemon juice. So, 30 - 12 = 18 members did not order lemon juice. Since 1 / 3 of the remaining ordered mango juice, then 18 x 2 / 3 = 12 members ordered mango juice. Therefore, 18 - 12 = 6 members ordered orange juice.
The answer: 6
Reverse engineering the question: A club with 30 members ordered fruit juices. Two-fifths of them ordered lemon juice. One-third of the remaining members ordered mango juice, and the rest ordered orange juice. How many members ordered orange juice?

The number of words that Carl can type per hour is 50 * 60 = 3000 words. The number of words that Carl can type in 4 hours is 3000 * 4 = 12000 words. The number of words that Carl can type in 7 days is 12000 * 7 = 84000 words.
The answer: 84000
Reverse engineering the question: Carl types at a speed of 50 words per minute. If he types continuously for 4 hours per day, how many words can he type in 7 days?

After the first spray kills 50% of germs, there will be 100 - 50 = 50% left. The second spray kills 25%, but 5% have already been killed by the 50% spray, so it kills 25 - 5 = 20%. After the second spray kills 20% of the remaining germs, there will be 50 - 20 = 30% left.
The answer: 30
Reverse engineering the question: A cleaning company produces two sanitizer sprays. One spray kills 50% of germs, and another spray kills 25% of germs. However, 5% of the germs they kill are the same ones. What percentage of germs would be left after using both sanitizer sprays together?

Monday, Wednesday, and Friday, Harry walks a total of 3 * 7 = 21 dogs. Thus, in a week he walks 21 + 12 + 9 = 42 dogs. At a rate of $5 per dog, Harry ears $5 * 42 = $210 per week.
The answer: 210
Reverse engineering the question:
Harry is a professional dog-walker. He is paid to go on long walks with dogs while their families are away from home. On Monday, Wednesday, and Friday, Harry walks 7 dogs. On Tuesday, he walks 12 dogs. And on Thursday he walks 9 dogs. He is paid $5 for each dog that he walks. How many dollars does Harry earn in a week?