The mean weight of 18 jackfruits is 7.2 kg. If the weights of 2 more jackfruits whose weights are equal are added. the mean weight decreases by 20g. What is the weight of each jackfruit added later? 

Correct option is C

Given:

Mean weight of 18 jackfruit = 7.2kg

Mean weight decreases by 20g if 2 more are added

Formula Used:

Average =$$\frac{\text{Sum of observations}}{\text{Number of observations}}$$​​

Solution:

Total weight of 18 jackfruits = 18 $$\times$$​7.2kg = 129.6kgs

Mean weight of 20 jackfruit after adding = 7200g - 20g = 7.180g

Total weight of 20 jackfruit = 20 $$\times$$​ 7.180 = 143.6kgs

Weight of 2 jackfruit added later = 143.6 -129.6 = 14kgs

Weight of each jackfruit =$$\frac{14}{2}$$ =7kgs

Alternative Method:

After adding 2 jackfruit mean decreased by 20g

Hence, total weight decreased by 20$$\times$$​ 20 = 400g

So each jackfruit decreased =$$\frac{400}{2}$$​= 200g

So weight of each jackfruit = 7.2kg - 0.2kg = 7kgs