Question

Diana had a large stack of playing cards. She knew that 17 of them were kings. She took a sample of 30 cards and found 4 kings. Approximately how many playing card did Diana have?

Answer 1

Diana approximately had 128 cards

Explanation:

Let n be the number of cards Diana had. She knows that

• there are 17 kings among n cards
• 4 kings among 30 cards

Write a proportion:

`(17)/(n)=(4)/(30)`

Cross multiply:

`4n=17\cdot 30\\ \\4n=510\\ \\n=(510)/(4)=127.5\approx 128`