# Thread: Finding a percentage of a quantity

1. ## Finding a percentage of a quantity

I'm wondering, because i'm doing this: 30% of 360m

I already know for example: 6%of $20 = 6/100 x 20/1 = 120/100 =$1.20
but when i'm doing: 30% of 360m = 30/100 x 360/1 (is that right? were mean't to be simplifying i think)

But when i multiply 30 by 360 i get: 10'800
How would i lay out my question! Because i'v converted the percentage and quantity to fraction.
Multiplyed and simplifyed (i hope)

And another one i'm puzzling over is: 75% of $1240 2. also i'm having trouble with this: I have to find the simple interest on:$620 at 8.5% p.a. for 2 years.

and $3500 at 9% p.a. for 3 years, 9 months. how would i do that? 3. Originally Posted by Sazza I'm wondering, because i'm doing this: 30% of 360m I already know for example: 6%of$20 = 6/100 x 20/1
= 120/100
= $1.20 but when i'm doing: 30% of 360m = 30/100 x 360/1 (is that right? were mean't to be simplifying i think) But when i multiply 30 by 360 i get: 10'800 How would i lay out my question! Because i'v converted the percentage and quantity to fraction. Multiplyed and simplifyed (i hope) And another one i'm puzzling over is: 75% of$1240

The hard way

30/100 x 360/1 = 30/10 x 36/1 = (multiply across) 108

The ease way to do this would be to just do:
.3 x 360 = 108
also
.75 x 1240 = 930 or using your method

75/100 x 1240/1 = 75/10 x 124/1 = 930

4. Originally Posted by nertil1
The hard way

30/100 x 360/1 = 30/10 x 36/1 = (multiply across) 108

The ease way to do this would be to just do:
.3 x 360 = 108
or simply 3 * 36. since 30/10 = 3

before actually multiplying the fractions, you want to cancel as much as possible to minimize difficulties in computation

5. also i'm having trouble with this: I have to find the simple interest on: $620 at 8.5% p.a. for 2 years. and$3500 at 9% p.a. for 3 years, 9 months. how would i do that?

6. Originally Posted by Sazza
also i'm having trouble with this: I have to find the simple interest on: $620 at 8.5% p.a. for 2 years. and$3500 at 9% p.a. for 3 years, 9 months. how would i do that?
$\displaystyle Simple \mbox { } Interest = Principal \times Rate \times Time$

Simple Interest is the interest we gain. the principal is the amount of money we start with. the rate is the percentage interest (written as a fraction) we gain per unit time and the time is how long we are earning interest for in terms of the number of interest periods

note that 3 years 9 months is 3.75 years