Question

Of the three numbers, the first is twice the second and the second is thrice the third. If the average of the three numbers is 10, the largest number is:
(a) 12
(b) 15
(c) 18
(d) 30

Answer 1

Hint:We will take the third number as some variable and then we are going to write second number in terms of third and first number is terms of second and then we will find the average of all the three number and equate it to 10, with that we will find all the numbers and then find out which one is the largest.

Complete step-by-step answer:
Let’s start by taking the third number as x.
Therefore the second number will be 3x.
And now we have found the second number in terms of x.
Therefore the first number will be $2\times 3x=6x$
Now we will find the average of all the three number,
Average will be,
$\begin{align}
  & \dfrac{x+3x+6x}{3}=10 \\
 & 10x=30 \\
 & x=3 \\
\end{align}$
Therefore,First number=3, the second number is 3x3 = 9 and the first number is 6x3 = 18.
So, from this we can see that the largest number is 18.
Hence the correct option is (c).

Note: One can also solve this question by taking some different variables and then do the same as given in the question. We will get the same answer. We can also take the first number as some variable and then find all the other numbers still we will get the same answer.Verify the answer by finding the mean of three numbers, whether we will get 10 or not.