Question

Average weight of a class is 60kg and average weight of boys in the class is 80kg. Ratio of boys to girls in the class is 5 : 4. If there are 72 students in the class, then find the average weight of girls in the class

Answer 1

Answer:

Correct option is

A

100,50

Total students in class =150

mean weight=60kg

total weight =150×60=9000kg

Let the total number of boys =x

mean weight of boys =70kg

total weight of boys =70×x=70xkg

total number of girls = total students - no. of boys =150−x

mean weight of girls=55kg

total weight of girls =55×(150−x)=55×150−55x=(8250−55x)kg

Total weight = weight of boys + weight of girls

9000=70x+(8250−55x)

9000=70x+8250−55x

9000−8250=70x−55x

750=15x

x=

15

750

x=50

So number of boys =50

number of girls =150−50=100

Answer 2

Answer:

The average weight of girls in the class = 35 kg.

Step-by-step explanation:

• In class number of boys: girls = 5:4

        Suppose the common factor is x

         Number of boys = 5x and number girls = 4x

        Total number of students = 5x + 4x = 9x

         According to the question, 9x = 72

                                                        x = 8

      In the class number of boys = 5 × 8 = 40 and

      number of girls = 4 × 8 = 32

• Weight calculation:

1) Total number of students = 72 and their average weight = 60 kg.

Total weight of all the students = 72 × 60 = 4320 kg

2) Total number of boys = 40 and their average weight = 80 kg.

      Total weight of all the boys = 40 × 80 = 3200 kg

3) Total number of girls = 32

   Total weight of all the girls = weight of the class - weight of boys

                                                 = 4320 - 3200 = 1120 kg

    Average weight of girls = $\frac{1120}{32}$ = 35

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