What number goes into both 75 & 390?

Question

Apart from 1

Okay thankz ppl. Just needed it for my maths homework, and I couldnt find the calculator:)

Answer 1

didny know there where that many brainy people

Answer 2

75 =3 x 5 x 5

390 = 2 x 3 x 5 x 13

You do these above calculations by trial and error.

75 ends in a 5, so it is divisible by 5

75 = 5 x 15

you already know 15 = 3 x 5

so 75 = 3 x 5 x 5

390 is divisible by 10 as it has a 0 at the end

390 = (2 x 5) x 39

The digits of 39 add up to 12, which can be divided by 3, so 39 can be divided by 3

390 = 2 x 5 x 3 x 13

13 is a prime number and cannot be divided by anything except 1 and itself

The calculations we have just done find the "factors" of the two numbers.

To find numbers that will divide into both, they need to appear in both groups of factors.

Do both numbers have 2 as a factor? No, so reject it.

Do both numbers have 3 as a factor? Yes, keep it

Do both numbers have a second 3 as a factor? No, so you can't include a second 3.

Do both numbers have a 5? Yes. A second 5, no so reject the second 5.

Only one number has a 13, so reject it.

The only factors appearing in both numbers are 3 x 5.

The HIGHEST number dividing into 75 and 390 is 15. It is called the Highest Common Factor of 75 and 390.

The other numbers dividing into 75 and 390 are 3, 5 and 1 of course.

Hope this helps.

Answer 3

5

Answer 4

5

Answer 5

15

Answer 6

15

Answer 7

15

Answer 8

15

Answer 9

3, 5 & 15

Answer 10

5?

Answer 11

3,5 n 15