Rounding off to Whole Numbers - Examples
2.00001 becomes 2
2.4999 becomes 2
2.5 becomes 3
2.999 becomes 3
BODMAS or BIDMAS
Brackets, Order, Division, Multiplication, Addition, Subtraction
Brackets, Index, Division, Multiplication, Addition, Subtraction
This is all about the order in which you do a calculation.
- B Anything inside brackets is always worked out first.
- O or I This is for items like Xy or 103 where y and 3 are the order or index. These are worked out after dealing with anything inside brackets.
- D Division and ...
- M ... multiplication are done next.
- A Lastly addition ...
- S ... and subtraction are done.
For example here are two bits of arithmetic with different meanings ...
3 + 2 x 7 = 17 Do the multiplication first and then add three.
(3 + 2) x 7 = 35 The brackets override the rule above so work out the brackets first and then multiply by seven.
Times Tables - Speed up your calculations by learning your times tables.
X |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
1 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
2 |
2 |
4 |
6 |
8 |
10 |
12 |
14 |
16 |
18 |
20 |
22 |
24 |
3 |
3 |
6 |
9 |
12 |
15 |
18 |
21 |
24 |
27 |
30 |
33 |
36 |
4 |
4 |
8 |
12 |
16 |
20 |
24 |
28 |
32 |
36 |
40 |
44 |
48 |
5 |
5 |
10 |
15 |
20 |
25 |
30 |
35 |
40 |
45 |
50 |
55 |
60 |
6 |
6 |
12 |
18 |
24 |
30 |
36 |
42 |
48 |
54 |
60 |
66 |
72 |
7 |
7 |
14 |
21 |
28 |
35 |
42 |
49 |
56 |
63 |
70 |
77 |
84 |
8 |
8 |
16 |
24 |
32 |
40 |
48 |
56 |
64 |
72 |
80 |
88 |
96 |
9 |
9 |
18 |
27 |
36 |
45 |
54 |
63 |
72 |
81 |
90 |
99 |
108 |
10 |
10 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
110 |
120 |
11 |
11 |
22 |
33 |
44 |
55 |
66 |
77 |
88 |
99 |
110 |
121 |
132 |
12 |
12 |
24 |
36 |
48 |
60 |
72 |
84 |
98 |
108 |
120 |
132 |
144 |
Calculate 1/4 + 1/7
Using a calculator with brackets you would enter this ...
1 / 4 + 1 / 7 =
You don't need brackets because the BODMAS rules work without them.
Harder Fractions
Calculate Rt if the formula is this: 1 / Rt = 1 / R1 + 1 / R2
Using a calculator with brackets you would calculate Rt like this ...
1 / ( 1 / R1 + 1 / R2 ) =
If there are no + or - signs in the formula, rearranging is easy. Diagonal moves are allowed across the equals sign. This works for most of the formulas for Electronics AS and A2.
Here is an example ...
Powers of Ten - Examples - The powers add up.
103 x 104 = 107
10-3 x 104 = 10
100 = 1
10-3 x 10-2 = 10-5
1 / 103 = 10-3
Some of these problems can be hard. There seem to be several different methods used by different calculator manufacturers to solve powers of 10. Most students should use a good but cheap basic specification scientific calculator. More advanced models can be too hard to use and sometimes are quite non-standard. Find out how to enter powers of 10 into your calculator. The most obvious way is nearly always wrong! Look for the Exp button. This is the "Times ten to the" button. Look for the +/- button. This is used to enter things like 10-9. If you use the normal minus button, on many calculators, it won't work.
If the frequency in Hertz = 1 / (2 π R C), to the nearest Hertz, calculate the frequency if R = 84 kilohms and C = 3 nanoFarads.
84 kilohms = 84 x 103 Ohms
3 nanoFarads - 3 x 10-9 Farads
Here are the calculator key presses for the calculators in our lab ...
1 / ( 2 x PI x 84 Exp 3 x 3 Exp 9 +/- ) =
Your calculator may be different. Learn how to use it! Get help if you need it!
