|
Directed
numbers
Clement
Radcliffe, Contributor
 |
| Students
of William Knibb Memorial High School, Trelawny, take notes during day two of
The Gleaner's Youthlink CSEC seminar in Montego Bay, in April. - Tashieka Mair/Freelance
Photographer | As
we continue our review of Directed Numbers, you are invited to look at the answers
to the problems given for Homework last week.Evaluate the following:
1) -4 x -3
= 12 -21 ÷ 3 = -7 2)
-18 -10 + 6 = -22 5a x -4b = -20ab 3)
12/25 x 5/9 ÷ 5/18 = 12/25 x 5/9 x 18/5
= 24/25 4)
11/12 + 5/6 -2/3 (Please
note that the LCM of 12, 6 and 3 is 12)
| = (1 x
11) + (2 x 5) - (4 x 2) = | 13 |
| 12 | 12
| If
the above posed no difficulty, then you are ready to consider exam-type questions.
Application
of the Four Arithmetic Operations to Vulgar Fractions In
applying the four basic operations to vulgar fractions, students are required
to observe the correct law with respect to the order of operation as follows:
B -
Brackets
O
- Of (Multiply)
M
- Multiply
D
- Divide
A
- Add
S
- Subtract BOMDAS
identifies the order in which the operations should be carried out and must always
be obeyed. Let's
practise the use of BOMDAS. (a)
Practice 1 Calculate
the value of: 1 1/2 + 5 x 2 ÷ 1 2/3 We
do the multiplication first: 1
1/2+ 10 ÷ 1 2/3 We
then do the division: 1
1/2 + [10 x 3/5] =
11/2 + 6
= 7 1/2 (b)
Practice 2 8
x (2 1/3 + 1/2) We first do the brackets (although we are required to add): ie.
(2 1/3 + 1/2 ) = 7/3 + 1/2 . Using the L.C.M. of 2 and 3, that is 6, we get To complete
the problem, we now multiply: 8
x 17/6 = 683 = 22 2/3 (c)
Practice 3 Calculate
the value of:
| 4 1/3
- 1 5/6 | | | 1
3/7 x 2 2/3 | | The
line represents brackets and so the numerator may be evaluated first. 4
1/3 - 1 5/6 = 13/3 - 11/6
Evaluating
the denominator: 13/7
x 2 2/3 = 10/7 x 8/3 = 80/21 Dividing
= 15/6
÷ 80/21 = 15/6 x 21/80 = 21/32 Points
to note - In
solving a problem such as Practice 3, you may first evaluate either the numerator
or the denominator.
- Finding
the L.C.M. CORRECTLY is a very important step in the solution.
- As
practice 3 requires the exact value, you are not allowed to express the fraction
in decimal form. If this is done, then your answer would be different from 21/32
and you may be penalised.
- Your
working must always be clearly shown in logical sequence.
I
close this week with the following: 1.
Calculate the value of 2 1/3 - 1 1/2, expressing your answer as a fraction. 2.
Evaluate: 16 x 5 ÷ 8 25 7 25 3
Simplify (2 1/3 ÷1 5/8) ÷ 1 1/3
4. Find the value of: 18.75 - (2.11)²
(No.
1 (a) (ii), CXC January 2006)
5. Find the value of:
2
1/4 x 4/5
3/5
- 1/2 (No.
1 (a) (i), CXC January 2006) Finally,
let me recommend that you keep all of these lessons together in a scrap book so
that you can always refer to them. If you require previous copies you should be
able to access these from the Gleaner Company. Clement
Radcliffe teaches at Glenmuir High School. | 
