30% of the pupils in a class are boys.there are 21 girls.how many pupils are there in the class in all?
0.7x = 21
x = 30
30 - 21 = ?
To find out the total number of pupils in the class, we need to determine the number of boys and then add it to the number of girls.
Given that 30% of the pupils in the class are boys, we can start by calculating the percentage as a fraction:
30/100 = 3/10
Let's say the total number of pupils in the class is x. We can then express the number of boys as 3/10 of x:
Number of boys = (3/10) * x
Now, we are given that there are 21 girls, so we can set up the equation:
Number of girls = 21
To find the total number of pupils, we can sum the number of boys and girls:
Number of boys + Number of girls = Total number of pupils
Substituting the expressions we found earlier:
(3/10) * x + 21 = Total number of pupils
Now, we can solve this equation to find the value of x, which represents the total number of pupils.