Question

Meena can type 500 words in 10 minute and Leena can type 400 words in 10 minutes. can type 3600 words in how many minutes? \[\]
A.50 minutes\[\]
B.40 minutes \[\]
C.80 minutes\[\]
D. 100 minutes \[\]

Answer 1

Hint: We use direct variation of unitary method and find the number of words Meena and Leena that can separately type in 1 minute. We can find the number of words that can be typed in 1 minute together by Meena and Leena and use it to divide the given number of words 3600 to find the answer.

Complete step-by-step answer:
We see that the number of words increases with the number of minutes. So the problem is in direct variation. We divide to get the value of a single unit. \[\]
We are given the question that Meena can type 500 words in 10 minute. So the number of words Meena can type in 1 minute is $\dfrac{500}{10}=50$ words.\[\]
We are also given the question that Leena can type 400 words in 10 minutes. So the number of words Leena can type in 1 minute is $\dfrac{400}{10}=40$ words.\[\]
The number of words they can type together in 1 minute is the sum of words Meena and Leena can type which is $50+40=90$words.
So 90 words can be typed by both Meena and Leena in 1minute. Then 3600 words can be typed by Leena and Meena in $\dfrac{3600}{90}=40$ minutes. \[\]

So, the correct answer is “Option B”.

Note: We know that the unitary method is a technique for solving a problem by first finding the value of a single unit, and then finding the necessary value by multiplying or dividing by the single unit value. When one quantity $a$ increases with another quantity $b$ and also $a$ decreases with $b$ then we say the quantities $a$ and $b$ are in direct variation. We should not try to solve by finding the number of minutes per word because word typing is measured in rate of typing. We can also make mistakes by finding Meena’s time for 3600 words and Leena’s time for 3600 words and then adding which is incorrect.