If a code word is defined to be a sequence of different letters chosen from the 10 letters A, B, C, D, E, F, G, H, I and J, what is the ratio of the number of 5-letter code words to the number of 4-letter code words?
a. 5 to 4; b.3 to 2; c. 2 to 1; d. 5 to 1; e. 6 to 1

I solved this problem as follows:
C (10;5) = 14 * 18
C (10; 4) = 14 *15
--> the ratio of the number of 5-letter code words to the number of 4-letter code words = (14*18)/(14*15) = 6/5

Please explain why the answer is 6 to 1????


Company S produces two kinds of stereos: basic and deluxe. Of the stereos produced by Company S last month, 2/3 were basic and the rest were deluxe. If it takes 7/5 as many hours to produce a deluxe stereo as it does to produce a basic stereo, then the number of hours it took to produce the deluxe stereos last month was what fraction of the total number of hours it took to produce all the stereos?
a. 7/17; b.14/31; c.7/15; d.17/35; e.1/2

Please show me how to solve this problem quickly???

Thank you!!!