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 Post subject: help with fractions
PostPosted: Tue Feb 24, 2009 9:30 pm 
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Joined: Tue Oct 28, 2008 10:05 pm
Posts: 100
Hello, please could anybody help me with this: calculate 3/8 of 980. I'm sure it's very simple but i'm no good and i'm hoping I can show your reply to dd.

this is year 6 homework and I think it may be a sats type of question as the sheet is from the LA assessment team

many thanks

b


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PostPosted: Tue Feb 24, 2009 9:42 pm 
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Joined: Mon Oct 06, 2008 1:41 pm
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Location: South Wilts
Calculate 3/8 of 980

Divide 980 by 8 = 122.5
Multiply by 3 = 367.5

or
Multiply 980 by 3 = 2940
Divide by 8 = 367.5

Remind her that fraction questions are division sums when concerning the denominator (bottom number), and multiplying sums when concerning the numerator(top number), or in this case a bit of both!


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PostPosted: Tue Feb 24, 2009 9:45 pm 
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Joined: Mon Feb 12, 2007 1:21 pm
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1/8 of 980 means 980 divided by 8 = 122.5

so 3/8 means 3 x 122.5 = 367.5


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PostPosted: Tue Feb 24, 2009 9:49 pm 
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Joined: Tue Oct 28, 2008 10:05 pm
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many thanks from me & grateful dd sycamore!


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PostPosted: Thu Feb 26, 2009 10:38 am 
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Joined: Thu Jan 12, 2006 3:29 pm
Posts: 625
Hi

When you see "of" in a fraction sum, this means "times", so 3/8 of 980 means 3/8 x 980.

An alternative method for multiplication of fractions is to reduce the numbers down.

3/8 x 980

The 8 and 980 can be halved, giving

3/4 x 490

The 4 and 490 can be halved, giving

3/2 x 245

The top line in a fraction are multiplied giving,

3 x 245 = 735

and this is divided by the number in the bottom line giving,

735 divided by 2 = 367.5

Here is another example of cancelling down fractions:

8/9 x 15/32

You cancel down any top number with any bottom number

8 and 32 can be cancelled, by halving, to 4 and 16, then 2 and 8, then 1 and 4, giving

1/9 x 15/4

9 and 15 can be cancelled down, by dividing by 3, to 3 and 5, giving

1/3 x 5/4

Multiply top line, then bottom line gives the answer,

5/12

Regards

Mike


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PostPosted: Thu Feb 26, 2009 1:45 pm 
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Joined: Tue Oct 28, 2008 10:05 pm
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Thanks Mike & guest 55


I will show your replies to dd when she gets home!

b


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