EXERCISES OF UNIT 3: "Divisibility" 1st ESO

1.- Write down:

a) The five first multiples of 11.

b) All the multiples of 20 between 150 and 210.

c) A multiple of 13 between 190 and 200.

d) All the even numbers whose product equals 80.

e) All the factors of 80.

2.- Find out all the factors of:

a) 10 b) 18 c) 20 d) 24

e) 30 f) 39 g) 45 h) 50

3.- Change each letter by a digit, so that the resulting number is divisible by 3 :

a) A51 b) 2B8 c) 31C d) 52D e) 1E8

4.- Decompose these numbers in prime factors:

a) 120 b) 285 c) 350 d) 105 e) 209 f) 323

5.- Find out which of these numbers are prime and which are composite:

14, 17, 28, 29, 47, 53, 57, 63, 71, 79, 91, 99

6.- For each diagram below:

a) List the numbers in the outer circle that are multiples of all the numbers in the inner circle.

b) Write down the lowest common multiple of the numbers in the inner circle; this may not be one of the numbers in the outer circle.

                             

7.- For each diagram below:

a) List the numbers in the outer circle which are common factors of all the numbers in the inner circle.

b) Write down the highest common factor of the numbers in the inner circle; this may not be one of the numbers in the outer circle.

                         

8.- Calculate the lcm and the hcf of these numbers:

a) 5 and 11 b) 4 and 18 c) 75 and 100

d) 2, 4 and 8 e) 10, 15 and 20 f) 20, 30 and 40

9.-­‐  Riddles:                          

10.-­‐  Riddles: