help with fractions

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40
Posts: 100
Joined: Tue Oct 28, 2008 11:05 pm

help with fractions

Post by 40 »

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
sycamore
Posts: 686
Joined: Mon Oct 06, 2008 2:41 pm
Location: South Wilts

Post by sycamore »

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!
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Post by Guest55 »

1/8 of 980 means 980 divided by 8 = 122.5

so 3/8 means 3 x 122.5 = 367.5
40
Posts: 100
Joined: Tue Oct 28, 2008 11:05 pm

Post by 40 »

many thanks from me & grateful dd sycamore!
Mike
Posts: 625
Joined: Thu Jan 12, 2006 4:29 pm

Post by Mike »

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
40
Posts: 100
Joined: Tue Oct 28, 2008 11:05 pm

Post by 40 »

Thanks Mike & guest 55


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

b
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