PROBABILITY---

Probability Level 1

From 1,2,3,...,250, one number is selected at random. What is the probability that it is either a multiple of 5 or a multiple of 4?

NOTE: Give your answer as a decimal.


The answer is 0.4.

Aman Vats by aman vats , 25, India

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2 solutions

Aman Vats
Mar 29, 2015

Number of multiples of 5=50 Number of multiples of 4=62 Number of numbers which are multiples of both 4 and 5 =12 Thus , P (selecting either a multiple of 5 or a multiple of 4)= =50/250+62/250-12/250 =100/250 =2/5 =0.4

5 Helpful 0 Interesting 0 Brilliant 0 Confused

Why are the number of multiples of 4 = 62 and not 60?

Lauren He - 3 years, 9 months ago

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Given two number 'N' and 'x', the number of multiple of 'x' from 1, .., N is floor(N/x)

Rômulo Rodrigues - 3 years, 2 months ago

And multiples from 1....250 for 4 are 250/4=62.25=62 because we are taking the whole no.s

Jai Malhotra - 3 years, 1 month ago

How do you calculate the number of numbers which are multiples of both 4 and 5?

Laurens Eikendal - 3 years, 1 month ago
Tehillah _
May 8, 2018

You can do it in an easy way, assume the nos. from 1 to 10, and find the multiples of 4 or 5 and then find the probability.

2 Helpful 0 Interesting 0 Brilliant 0 Confused

If you choose 1 to 10 or 1 to 20 or 1 to 30 or....or 1 to 250, you will always find 0.4.

Pierre Morin - 2 years, 11 months ago

I am not sure examples are sufficient proof. Maybe a proof by induction is required.

Reshandre katz - 2 years, 9 months ago

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