Exercise 1: Counting binary strings. Count the number of binary strings of length 10 subject to each of the following restrictions. There is only one binary string of length ten with no 1's: 00000000000. There are 2^{10} binary strings of length ten. How many integers in the range 1 through 140 are integer multiples of 2, 5, or 7?

Elleanor Mckenzie

Elleanor Mckenzie

Answered question

2021-07-30

Exercise 1: Counting binary strings.
Count the number of binary strings of length 10 subject to each of the following restrictions.
There is only one binary string of length ten with no 1's: 00000000000. There are 210 binary strings of length ten. Therefore the number of binary strings of length ten with at least one 1 is 2101.
(b) The string has at least one 1 and at least one 0.
(c) The string contains exactly five 1's or it begins with a 0. 


Exercise 2: Counting integer multiples.
(b) How many integers in the range 1 through 140 are integer multiples of 2, 5, or 7?

Answer & Explanation

komunidadO

komunidadO

Skilled2021-07-31Added 86 answers

There is at least one 1 and at least one 0 in the string. As a result, both all ones and all zeros are eliminated. 2102 is the total amount of binary strings. 

The string contains exactly 5 1s

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