percentages? 20 of?

Question

a, a table is priced at £12 but during a sale, all prices are reduced by 20%. how much does the table cost now?

b, the height of a tree increases by 15%. if it was 3 meters high before, how high is it now?

how do i calculate theses? what are the stages?

Answer 1

a. multiply 12 by 80% (0.80) to get the cost)

c. multiply 3 by 1.15

Answer 2

Percentages are 'units per hundred'...

So if an item increases or decreases by a fixed percentage, the fixed percentage must be applied to 1/100th of the original size (or price)

In your first example.

The table is £12 but it is reduced by 20% in the sale.

Divide the original amount by 100 = £12/100 = 12 pence as there are 100 pence in the pound.

Now multiply the 12 pence by 20 to give you 20% = £2.40

As the table was reduced by twenty percent, you subtract £2.40 from £12 to give you £11.60.

The other way to do this (and a bit faster if you have a calculator) is to use decimal fractions.

Imagine that anything you wish to divide up is a single unit of 1. Divided by 100, the 1 becomes 100 equal parts of 0.01.

Subtract 20 from 100 and you get 80.

20% off the price will mean the cost is now 80% of the original.

80x 0.01 = 0.8

So by multiplying £12 by 0.8, you also get £11.60

You can represent any percentage this way.

75% = 0.75

33% = 0.33

Just remember that if you have something that is 15% bigger, you add the 15% on to the original and if it's 15% smaller, you take the 15% off the original.

As for your second question,

Tree = 3m = 300cm

Adding 15% = 300 + (300x0.15) = 300 + 45 = 345cm

or 3.45m

and using the original method of dividing it all by 100...

3m = 300cm

300/100 = 3cm (this equals 1% of 3m)

15% = 3cmx15 = 45cm

As the tree has grown, you add the 45cm to the 300cm to give 345cm or 3.45m

Answer 3

A - 20% is always 1/5 so simply divide by 5 and then subtract the answer from the original number - in this case 12.00 / 5 = 2.4
price of table 12.00 - reduction 2.40 = 9.60

B - work out 1% by dividing the height of the tree by 100 3cm
Mutiply by 15 =45cm
total tree height 3.45m

Answer 4

To find 10% of £12.00 just move the decimal point 1 place to the left which gives you a figure of £1.20. For 20%, times £1.12 by 2 giving an answer of £2.24.

With 3 metres, again move the decimal point 1 place to the left giving a figure of .3 plus 1/2 of that for the 5% giving a figure of .15, add these together for 15% and you have .45. Add .45m to the 3m and you have 3.45m (just under three and a half metres.,

Answer 5

Present cost of table:
L12.00 * (100% - 20%) = L12.00 * 80% = L9.60

Answer: The cost of table now is L9.60.

Present height of a tree:
3 m * (100% + 15%) = 3 m * 115% = 3.45 m

Answer: The height of the tree now is 3.45 meters.

Answer 6

a)...20% = 80% of original price. (£12.00)
80% = 80/100 = 0.80
0.80 x £12 = £9.60.
b)...3m = 100% (original height)
New height = 115%
115% = 115/100 = 1.15.
New height = 1.15 x 3 = 3.45m = 3m 45cm

The difference in the calculations is that, in 1). It's a reduction and, in 2). it's an increase).

Answer 7

20% = 1fifth 1/5 so find 1/5 of £12 and deduct this from £12

Answer 8

a: £9.60 10% is £1.20 x2 = 20% = £2.40 so take that off to get £9.60

b: 3.45 15% of 1m =.15 x 3 for 3 meters

Answer 9

a.20/100 x 12= 12/ 5= 2.4
12-2.4= £9.60

b. 15/100x 3= 0.45m
3.45m

Answer 10

Table Q

To calculate this I would take the £12.00, divide by it by 5 (which would give you 20%) and then subtract that;

£12.00 / 5 = £2.40........ £12.00 - £2.40 = £9.60

Tree Q

3m / 100 * 15 = 0.45m....... 3m + 0.45m = 3.45m

There's probably an easier way, but this is how I remember being taught it.

Answer 11

Question a.
Reduction = (20 / 100) x £12 = £240 / 100 = £2.40
OR
10%<---->£1.20
20%<---->£2.40
Will now cost £12 - £2.40 = £9.60
OR
Reduced price is 80% of £12
= ( 80 / 100) x £12
= £9600 / 100
= £9.60

Question b.
10%<---->0.3 m
5%<----->0.15 m

15%<---->0.45 m

Tree is now 3.45 m