b. Salt it. Another strategy is to start with a word or phrase that is easy to r
ID: 3183182 • Letter: B
Question
b. Salt it. Another strategy is to start with a word or phrase that is easy to remember and then add some random changes to it. Bob starts with Superman and then applies one modification to it where a modification consists of inserting a number at some position. This process can produce a string like Super5man bl. How many different strings can Bob create starting with Superman? Suppose Bob wants to apply two modifications to produce a string like 9Supersman or a string like Super95man. We want to determine the dif ferent strings Bob can create. He does this in two steps: Step 1 Choose the first number say 5) and insert it in Superman. (It produces Super5man, etc.) Step 2. Choose the second number (say 9) and insert it in the string obtained after Step 1. (If the string from step 1 was Super5man, then the result can be 9Super5man or Super95man, etc.) b2. To determine the number of different strings Bob can create, we can just apply the Product Rule (Handout 8, page 3). Explain why the productExplanation / Answer
a) he can create 10C1 x 9 different strings of super man with single digit in it
we have to select1 number out of 10 in 10C1 ways = 10; and 9 positions in the word superman.
so totally we have 90 strings.
b) we have to select 2 out of 10 numbers in 10C2 ways = 45 ways.
I have to keep 2 numbers in 9 x 2 = 18 ways .
totally we have 45 X 18 = 810 strings
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