Question

A pineapple costs Rs. 7 each. A watermelon costs Rs. 5 each. X spends Rs. 38 on these fruits. The number of pineapples purchased is
A. 2
B. 3
C. 4
D. Data inadequate

Answer 1

Hint: Cost of a pineapple is Rs. 7 and cost of a watermelon is Rs. 5. X spends Rs. 38 on these fruits. The cost of ‘m’ pineapples is Rs. 7m and the cost of ‘n’ watermelons is Rs. 5n. The total amount on these fruits is $ 7m + 5n = 38 $ . Solve the equation to get the no. of pineapples ‘X’ purchased.

Complete step-by-step answer:
We are given that the cost of each pineapple is 7 and the cost of each watermelon is 5.
X spends 38 rupees to buy both these fruits. We have to find the no. of pineapples ‘X’ purchased.
Let the no. of pineapples ‘X’ purchased is ‘m’ and the no. of watermelons ‘X’ purchased is ‘n’
The total cost X spent is $ 7m + 5n $ rupees
 $
  \therefore 7m + 5n = 38 \\
   \to 7m = 38 - 5n \\
   \to m = \dfrac{{38 - 5n}}{7} \\
  $
The no. of pineapples purchased should be a whole number. So 38-5n should be a multiple of 7 to get a whole number.
Only when n is 2, the no. of pineapples purchased will be a whole number. Therefore n=2.
The value of m is
 $
  m = \dfrac{{38 - 5\left( 2 \right)}}{7} \\
  m = \dfrac{{28}}{7} \\
  m = 4 \\
  $
The no. of pineapples purchased is 4 and the no. of watermelons purchased is 2.
So, the correct answer is “Option C”.

Note: We solved the problem by trial and error method. Trial and error is a fundamental method of problem-solving. It is implemented by repeated, varied attempts which are continued until success, or until the solver stops trying. An efficient number of trials must be done to avoid time and energy wastage.