Explain the meaning of the accompanying percentiles.
(a) the 15th percentile of the head circumference of males 3 to 5 months of age in a certain city is 41.5 cm.
(b) the 90th percentile of the waist circumference of females 2 years of age in a certain city is 52.7 cm.

Part A) The 15th percentile of the head circumference of males 3 to 5 months of age in a certain city is 41.5 cm.

Percentile : A data item is said to be in nth percentile of distribution if n% of the distribution are less than that particular data item.

So, by definition we can say that the given statement means that 15% of males of 3 to 5 months of age have a head circumference less than or equal to 41. 5 cm

Part B ) The 90th percentile of the waist circumference of females 2 years of age in a certain city is 52.7 cm.

Percentile :  A data item is said to be in nth percentile of distribution if n% of the distribution are less than that particular data item.

So, by definition we can say that the given statement means that The 90th percentile means that 90% of females of 2 years of age have less than or equal to 52.7 cm for their waist circumference

walter needs to make at least 5 more cookies but no more than 40. 5 ≤ x ≤ 40

step-by-step explanation:

20 ≤ x + 15 ≤ 55

subtract 15 from all parts

20-15 ≤ x + 15-15 ≤ 55-15

5 ≤ x ≤ 40

this means how many more cookies he has to make

walter needs to make at least 5 more cookies, but no more than 40 cookies; 5 ≤ x ≤ 40

step-by-step explanation:

1. practice, practice & more practice

2. review errors

3. master the key concepts

do not try to memorise the processes.

4. understand your doubts.

5. create a distraction free study environment

6. create a mathematical dictionary

7. apply maths to real world problems.