Question

A typist can type 45 words per minute. He increases his speed by 20 per cent. How many words can he now type per hour?
a. 3210
b. 3240
c. 3270
d. 3300

Answer 1

Hint: We will first find the new speed, so we will take 20% of 45 by using the formula, $ \dfrac{20}{100}\times speed $ , then we will add 45 with 20% of 45 and then finally we will calculate the speed of the typist per hour as, $ \left( 45+20\%of45 \right)\times 60 $ .

Complete step-by-step answer:
It is given in the question that a typist can type 45 words per minute. He increases his speed by 20 per cent. And we have been asked to find the number of words he can now type in an hour.
So, the initial speed of the typist is 45 words per minute. And it is given that he increases his speed by 20%, so we can write 20% of the initial speed, that is 20% of 45 as,
 $ \dfrac{20}{100}\times 45=0.2\times 45=9 $
So, with his increased speed he can now write an extra of 9 words per minute along with the 45 words. So, the new speed of the typist is,
45 + 9 = 54 words per minute
It means that the new typist can now type 54 words per minute.
We know that 1 hour = 60 minutes. So, the typist can type $ \left( 54\times 60 \right) $ words in one hour, which is equal to 3240 words.
Thus, the typist can type 3240 words per hour.
So, option (b) is the correct answer.

Note: Most of the students make mistakes as they consider 9 as the new speed of the typist and forget to add it with 45, as a result, they get the speed of the typist in 1 hour as $ 9\times 60=540 $ words, but we know that it is wrong. So, it is recommended that the students solve this question carefully.