Download Fractions, and your Calculator – first page Why bother with LCMs

Fractions, and your Calculator – first page
Why bother with LCMs and all that?
If you want to get 1/8 + 3/10 you can do either of:

LCM Method
find the LCM(8,10) = 40 and convert both fractions to 40ths.
5/40 + 12/40 = 17/40

Product Method
8 and 10 will definitely divide into 80 = 8 x 10 evenly, so convert them both to 80ths
10/80 + 24/80 = 34/80 = 17/40
The second method will often involve more work to simplify the answer. There is a good reason
for the LCM method, if you’re adding or subtracting lots of fractions at the same time, but if
you’re only adding two then the product method can be much faster:
1/3 + 1/2 - 2/3 + 1/4 - 1/6

LCM(3,2,3,4,6) = 12 leads to 4/12 + 6/12 – 8/12 + 3/12 – 2/12 = 3/12 = 1/4

Product Method leads to 144/432 + 216/432 - 288/432 + 108/432 – 72/432 =
108/432 = 1/4
Calculator
On the Casio fx – 83 ES there is a button with a white rectangle over a line with the outline of a
white rectangle below the line. It’s for entering fractions, press this and the blue circular up
down left right button to put in fractions.
To put in 2/5 + 1/3 press: fraction button, 2, down arrow, 5,right arrow, +, fraction button, 1,
down arrow, 3, right arrow,=

If you’re completely lazy just try: 2, divide, 5 ,+, 1, divide, 3, =
on the screen but it works.
it doesn’t look as pretty
Fractions, and your Calculator – second page
MULTIPLYING FRACTIONS
This is much easier than adding them; just multiply the two top numbers and multiply the two
bottom numbers. Convert the fraction to one number / another number first. (5/2 Not 2 ½)
1/3 x 2/5 = 2/15;
¾ x ¾ = 9/16; 23/245 x 56/31 = 1288/7595;
2/3 x 5 = 2/3 x 5/1 = 10/3
DIVIDING FRACTIONS
To divide by a fraction, turn it upside down and multiply by it.
2/3 divided by 1/6
= 2/3 x 6/1 = 12/3 = 4/1 = 4
1)How many half pizzas are there in three pizzas?
3 divide by ½ = 3 x 2/1 = 3/1 x 2/1 = 6/1 = 6
2) A teenager will eat two and a half pizzas. How many teenagers can be feed from 10 pizzas?
3) 20m2 of grass needs 1kg of fertilizer. How much fertilizer does 5m 2 require?
4) Seven people each put 3/4 of a kilogramme of sand into a bucket. How much sand is in the
bucket?
5a) 5/6 x 3/10 =
5b) 4/7 x 3/8 =
5c) 12/25 x 10/16 =
5d)1/2 x 1/2 x 1/2 =
5e) 1/2 x (2/3 + 3/4) =
5f) 32 divided by ½ =
5g) 1/6 + (2 x 1/3) =
5h) ½ + ¼ + 1/8 + 1/16 =
Answers to Fractions and Your Calculator
2) 10 divided by 2 and a half = 10 /(2 ½ ) = 4
3) 4/20 = ¼ = 250grammes
4) 7 x ¾ = 21/4 = 5 and ¼ = 5.25kg
5a) 15/60 = 1/4
5b) 12/56 = 3/14
5c) 120/400= 3/10 = 0.3
5d)1/8
5e) 1/2 x (17/12) =17/24
5f) 32/1 x 2/1 = 64/1 = 64
5g) 1/6 + (2 /3) = 5/6
5h) 15/16
Answers to Fractions and Your Calculator
2) 10 divided by 2 and a half = 10 /(2 ½ ) = 4
3) 4/20 = ¼ = 250grammes
4) 7 x ¾ = 21/4 = 5 and ¼ = 5.25kg
5a) 15/60 = 1/4
5b) 12/56 = 3/14
5c) 120/400= 3/10 = 0.3
5d)1/8
5e) 1/2 x (17/12) =17/24
5f) 32/1 x 2/1 = 64/1 = 64
5g) 1/6 + (2 /3) = 5/6
5h) 15/16