Question
A person starts multiplying consecutive positive integers starting from 20. How many numbers should he multiply before he will have a result that will end with 3 zeroes?
Answer: Option C
:
C
A number will end in 3 zeroes when it is multiplied by three 10s.
To get a 10, one needs a 5 and a 2.
20=2×10⟹20 will give one zero and it has one extra 2.
So, to get three zeroes he should multiply till he encounters two more 5s and one more 2.
Since 25 has two 5s and 22 has one 2 ⟹ he should multiply till 25 i.e. 20, 21, 22, 23, 24, 25 = 6 numbers.
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:
C
A number will end in 3 zeroes when it is multiplied by three 10s.
To get a 10, one needs a 5 and a 2.
20=2×10⟹20 will give one zero and it has one extra 2.
So, to get three zeroes he should multiply till he encounters two more 5s and one more 2.
Since 25 has two 5s and 22 has one 2 ⟹ he should multiply till 25 i.e. 20, 21, 22, 23, 24, 25 = 6 numbers.
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