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NUMBER THEORY AND CRYPTOGRAPHY QUIZ - UNIT 1 & 2

Total questions: 20

Worksheet time: 15mins

Name
Class
Date
1.

If a|b and b=aq+r, then

a)

r=0

b)

0 < r < a

c)

0 <= r < a

d)

0 <= r <= a

2.


If g=(a,b), d|a,d|b then

a)

d | g

b)

g | d

c)

a| g

d)

b | g

3.

If (x/g,y/g)=1 then (x,y)=

a)

1

b)

(x/g , y/g)

c)

g

d)

(g/x , g/y)

4.

For any integers x,y, the least positive of the form ax+by =

a)

1

b)

(a, b)

c)

[a, b]

d)

(a, b) [a, b}

5.

a*b=

a)

(a,b) [a,b]

b)

(a,b) /[a,b]

c)

[a,b]/ (a,b)

d)

(a,b) +[a,b]

6.

The Factoring of any integer n>1 into primes is unique apart from the order of prime factors.

a)

Fundamental theorem of Number theory

b)

Fundamental theorem of Arithmetic

7.

If (a, b) = 11, [a, b] = 693 and a = 77 then b =?

a)

11

b)

99

c)

66

d)

33

8.


For any odd integer n, n ≡ 1 or −1(mod 2) 

a)

false

b)

true

9.


If b ≡ c ( mod m) then (b, m)= 

a)

(b+c , m)

b)

(b-c , m)

c)

(b, m)

d)

(c, m)

10.

If p is prime  a(p−1) ≡ ________ (mod p)​ 

a)

1

b)

0

c)

-1

d)

a

11.

If (a, m)=1 and  ax ≡ b (mod m) then x= ​ 

a)

aϕ(m)

b)

aϕ(m)-1

c)

aϕ(m)b

d)

aϕ(m)-1 b

12.

6! Ξ _______ ( mod 7)

a)

1

b)

-1

c)

0

d)

none of these

13.

If {a1​,a2​, ...,ar​} is a CRS mod m  then for any integer  y,  y ≡ a​i and aj​(mod m) i ≠ j  

a)

true

b)

false

14.

ϕ(m,n) = ϕ(m) ϕ(n)  for any integer n,m

a)

true

b)

false

15.

A set {a1​,a2​, ... ,ar​} is a RRS mod m  and for any integer y,  y ≡ ai​ (mod m) some i  if ___________

a)

(ai , aj) = 1

b)

(y, m) = 1

c)

(y, ai )=1 and (y, m) =1

d)

( ai , m) =1 and (y, m) = 1

16.

There are no large gaps in the series of primes

a)

True

b)

False

17.

If a = 2*5*7*2*3 and b = 3*3*5 then (a,b) =

a)

2*3*5*7

b)

3*3*5

c)

2*2*3*3*5*7

d)

3*5

18.

If a = 2*5*7*2*3 and b = 3*3*5 then [a,b] =

a)

2*3*5*7

b)

3*3*5

c)

2*2*3*3*5*7

d)

3*5

19.

(ma, mb) =

a)

(mb, ma)  

b)

m(a,b)

c)

both are true 

d)

none of these

20.

If p is prime, p| ab then    

a)

p|a and p|b

b)

p|a or p|b 

c)

p|a (only) 

d)

p|b (only)