11 Plus Exams Forum

Can people help please? I don't know what to start. The question is - The factors of a number add up to 13. What is the number? How do we do this please?

Thank you

Factors are 2 numbers which you multiply together to make a given number..

E.g factors of 12
are 1, 2, 3, 4, 6 and 12. ( 1x 12; 2x6; 3x4)

so for this you could find 2 numbers which add up to 13 and multiply them together.

There is more than one answer, was it a multiple choice question?

I think they want all the factors of a particular number, so start with 2:

the factors of 2 are 2 and 1 (2 is divisible by 2 and 1 only), so adding them together will get 3 (2+1=3)

then 3 - the factors are 3 and 1 only, so 3+1=4

for 4 - the factors are 4, 1 and also 2, because 4 is divisible by 2 also, so the sum of the factors will be 4+1+2=7

for 5 - the factors are 5 and 1 only, so 5+1=6
for 6 - the factors are 6, 1 and also 2 and 3, so 6+1+2+3=12
for 7 - the factors are 7 and 1 only, so 7+1=8
for 8 - the factors are 8, 1 and also 2 and 4, so 8+1+2+4=15
for 9 - the factors are 9, 1 and also 3, so 9+1+3=13 - BINGO!

hope that helps

Doh! How many times do I tell my pupils......

"Read The Question!"

The number must be less than 13 so I would have worked down from there ...
13 - can't be
12 - has lots of factors so not that
11 - no - it's prime so 11 + 1 = 12
10 - again too many factors
9 - yes, 1 + 3 + 9 = 13 (what do you notice about the sum of factors of a square number?)

Sorry everyone for late reply - Internet went for long spaces of time. DH thought it only worked when we asleep

I think we need to play with factors to get this. Your replies so helpful. Thank you

Lots and lots of board and dice games and interactive stuff online if you goggle factor games. I play them with my pupils, the competitive spirit takes over and they can spot them really quickly!

Eta: I meant google!

Thank you yoyo123. I look for them.

Please see Khan Academy videos on youtube. My DS was always confused till he saw those and now he is very confident/quick and accurate. You can see them for other topics as well.

Please don't use Khan Academy without being aware of the issues with it from a maths teacher's point of view.

I won't go on about it, as I've mentioned this before, but its American and uses non-UK methods and vocabulary. It's more likely to confuse than help.