## Monday, 14 July 2014

### Class Work 3(Tier C)

3. The median of a set of numbers is 4.5. Given that seven of the numbers are 9, 2, 3, 4, 12, 13 and 1, find the eighth number.

Let a be the unknown eighth number.

Numbers in ascending order
1, 2, 3, 4, 9, 12, 13

4 is the median of the seven numbers.

4.5 = 4 + a
2
4.5 x 2 = 4 + a
9 = 4 + a
a = 5
The eighth number is 5.

4. A box contained five cards numbered 1, 2, 3, 4 and 5. A card was drawn from the box, its number noted and then replaced. The process was repeated 100 times and the table below shows the resulting frequency distribution.

Numbers              1        2        3        4        5
Frequency           21       x        y       18      17

(a) Show that x + y = 44
(b) If the mean of the distribution is 2.9, show that 2x + 3y = 112
(c) Find the value of x and y
(d) State the mode and the median of the distribution.

a)
The total frequency is 100 as the process was repeated 100 times.

100 = 21 + 18 + 17 + x + y
100 = 56 + x + y
44 = x + y

b)
2.9 x 100 = 290
21 x 1 + x x 2 + y x 3 + 18 x 4 + 17 x 5 = 178 + 2x + 3y
=  290
290 = 178 + 2x + 3y
112 = 2x + 3y

c)
Since 44 = x + y and 112 = 2x + 3y,
y = 112 - 44 x 2
= 112 - 88
= 24
x = 44 - 24
= 20

x = 20 and y = 24

d)
Numbers              1        2        3        4        5
Frequency           21      20      24      18      17

From this diagram we can tell that the mode is 3.

The median number will be the mean of the 50th and the 51st number.

Numbers which are 1 are the numbers from 1 to 21.
Numbers which are 2 are the numbers from 22 to 42.
Numbers which are 3 are the numbers from 43 to 66.
As 50 and 51 are in the range of numbers which are 3,
the median is 3.