Bunuel wrote:
If 20 typists can type 48 letters in 20 minutes, then how many letters will 30 typists working at the same rate complete in 1 hour?
A. 63
B. 72
C. 144
D. 216
E. 400
We can set up a proportion to determine the rate n (number of letters per minute) of 30 typists.
20 typists / rate of those 20 typists = 30 typists / (unknown) rate of those 30 typists
20/(48/20) = 30/n
20/(12/5) = 30/n
100/12 = 30/n
100n = 12 x 30
10n = 12 x 3
10n = 36
n = 3.6
We see that the rate of 30 typists is 3.6 letters per minute. So in 60 minutes, 30 typists can complete 3.6 x 60 = 216 letters.
Alternate Solution:
We know that 20 typists can type 48 letters in 20 minutes. Thus, we see that in 60 minutes, or 1 hour, those 20 typists can type 3 times as many letters, or 3 x 48 = 144 letters. We can now set up a proportion for n = the number of letters that can be typed in 1 hour by 30 typists:
20/144 = 30/n
20n = 144 x 30
2n = 144 x 3
n = 216
Answer: D
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