25 % of a class of 40 students are girls. When some new girls joined the class, the percentage of girls increased to 40 %. How many new girls are joined the class
Let's first find out how many girls are originally in the class.
25% of 40 students is (25/100) * 40 = 10 girls.
Now let's assume that 'x' new girls joined the class.
The total number of girls after the new girls joined is 10 + x.
The total number of students in the class is 40 + x (accounting for the new girls).
According to the problem, the percentage of girls increased to 40%.
So we have the equation:
(10 + x) / (40 + x) = 40/100 = 0.4
Cross-multiplying, we get:
0.4 * (40 + x) = 10 + x
16 + 0.4x = 10 + x
0.4x - x = 10 - 16
-0.6x = -6
Dividing both sides by -0.6, we get:
x = -6 / -0.6
x = 10
Therefore, 10 new girls joined the class.
To solve this problem, we can follow these steps:
Step 1: Calculate the initial number of girls in the class.
We know that 25% of the class are girls, so we can find the number of girls by multiplying 40 (total number of students) by 0.25 (25% written as a decimal).
Girls = 40 * 0.25 = 10 girls
Step 2: Determine the desired percentage of girls in the class.
We want the percentage of girls to increase to 40%, so we know that the total number of girls will be 40% of the updated class size.
Step 3: Calculate the updated class size.
To find the new class size, divide the number of girls by the desired percentage (40%) written as a decimal.
New class size = 10 girls / 0.40 = 25 students
Step 4: Find the number of new girls that joined.
To find the number of new girls who joined the class, subtract the initial number of girls from the total number of girls in the updated class.
Number of new girls = 25 girls - 10 girls = 15 new girls
Therefore, 15 new girls have joined the class.
25% of a class of 40 means there are
0.25*40=10 girls.
Let x new girls joined the class.
total number of girls = 10+x
total size of class = 40+x
Given girls now make 40% of class, then
(10+x)รท(40+x) = 0.40
Cross multiply and solve for x. Alternatively, solve by guess and check.