We have a question: Jack wants to send thank you cards to everyone who got him a gift for his wedding. He sent out 200 invitations. 90% of people RSVPed but only 80% of people who RSVPed actually showed up. Then 10 people who showed up didn't get a gift. How many thank you cards does he need?
And an answer: 134
So how you got the answer?
He got 200 * .9 = 180 RSVP. Of those only 180 * .8 = 144 people showed up. So only 144 - 10 = 134 got him gifts and hence need thank you cards.

We have a question: John took a test with 80 questions. For the first 40 questions, she got 90% right. For the next 40 questions, she gets 95% right. How many total questions does she get right?
And an answer: 74
So how you got the answer?
He gets 40 * .9 = 36 questions right for the first part. For the second part, he gets 40 * .95 = 38 questions right. So he gets a total of 36 + 38 = 74 questions right.

We have a question: Jake and Penny are hunting snakes. Jake's snake is 12 inches longer than Jenny's snake. If the two snakes have a combined length of 70 inches, how long is Jake's snake?
And an answer: 41
So how you got the answer?
Let j be the length of Jake's snake and p be length of Penny's snake. We know that j + p = 70, and j = p + 12. We can substitute the second equation into the first equation to get p + 12 + p = 70. Combining like terms, we get 2p + 12 = 70. Subtracting 12 from both sides, we get 2p = 58. Dividing both sides by 2, we get p = 58 / 2 = 29 inches. Penny's snake is 29 inches. Substituting that length in to the equation j = p + 12, we get j = 29 inches + 12 inches = 41 inches.