Help with a fractions question please!

11 Plus Maths – Preparation and Information

Moderators: Section Moderators, Forum Moderators

Post Reply
11 Plus Platform - Online Practice Makes Perfect - Try Now
naxa
Posts: 60
Joined: Thu Sep 04, 2008 11:48 am
Location: Finchley

Help with a fractions question please!

Post by naxa »

Can someone help me explain how to do this question which was on a practice test my son was given?

If 1/a + 1/b = 7/10
What are the values of "a" and "b"?

Personally I haven't a clue, so any help much appreciated!
srk13
Posts: 44
Joined: Mon Feb 09, 2009 2:12 pm

Post by srk13 »

1/a + 1/b = 7/10


1*b + 1*a ...........7
_________ = _____
a*b ....................... 10


a+b .................. ..................... 7
_____ ...................= ................. ______
a * b ........................................ 10

These being equivalent fractions


a+b = 7 and a*b = 10

If you now find factors of 10 such that they add upto 7, which is the answer

a, b will be 5,2
SunlampVexesEel
Posts: 1245
Joined: Fri Jul 06, 2007 9:31 pm

Post by SunlampVexesEel »

or by observing split into two terms...

7/10

is...

6/10 + 1/10 which is... 3/5 + 1/10... i.e. not of the form 1/a+1/b so ignore...

5/10 + 2/10 which is... 1/2 + 1/5... Looks Good

4/10 + 3/10 which is... 2/5 + 3/10... i.e. not of the form 1/a+1/b so ignore...

3/10 + 4/10 ... hang on... we've done this one so STOP.
Animis opibusque parati
naxa
Posts: 60
Joined: Thu Sep 04, 2008 11:48 am
Location: Finchley

Post by naxa »

Oh boy, don't think I will be able to explain it very easily with confusing my son! I guess the split terms method would be the easiest way to go, as he should at least know that the denominator has to be the same when adding fractions.

Do these types of questions come up very often in 11+ exams or can I just ignore it and hope for the best? (she asks, with fingers crossed)
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Post by Guest55 »

Which tests is he sitting?
naxa
Posts: 60
Joined: Thu Sep 04, 2008 11:48 am
Location: Finchley

Post by naxa »

He's sitting the exams for independent boys schools in London next January.
Post Reply