Question

The average of the first four of five numbers is 40 andthat of the last four numbers is 60. the difference of the lastand the first number is:

Answer 1

40*4+last one=first one +60*4
difference =80

Answer 2

Answer: The difference of last and first number is 80.

Step-by-step explanation:

Since we have given that

Average of first four of five numbers = 40

Let the numbers be a,b,c,d,e

So, it becomes,

$\dfrac{a+b+c+d}{4}=40\\\\a+b+c+d=160$

Average of last four numbers = 60

So, it becomes,

$\dfrac{b+c+d+e}{4}=60\\\\b+c+d+e=60\times 4\\\\b+c+d+e=240$

Difference between the two equations:

$(b+c+d+e)-(a+b+c+d)=240-160\\\\e-a=80$

Hence, the difference of last and first number is 80.