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A box contains 40 number tiles numbered 1 to 40. If a tile is drawn at random, what is the probability that the number drawn is a multiple of 3 or 4? Find P(Multiple of 4 or Multiple of 5)

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  • FelisFelis


    Explanation 1 P (3 or 4):

    There are 40 number tiles numbered 1 to 40.

    Multiple of 3 in 1 to 40 are:

    There are 10 multiples till 30 (since 3 \times 10 = 30) and then 33, 36, and 39 are other three multiples till 40. So there are 13 multiples of 3 from 1 to 40.

    Multiples of 4 in 1 to 40 are:

    There are 10 multiples till 40 (since 4 \times 10 = 40) . So there are 10 multiples of 4 from 1 to 40.

    Common Multiples of 3 and 4 in 1 to 40 is,

    12, 28, 36, only 3

    So, the probability of 3 or 4 is,

    P(\text {mult of 3})+P(\text {mult of 4}) -P(\text {mult of 3 and 4})

    =\frac{13}{40} +\frac{10}{40} -\frac{3}{40}

    =\frac{23}{40} -\frac{3}{40}

    =\frac{20}{40}

    =\frac{1}{2}

    So the probability of 3 or 4 is \frac{1}{2}.


    Explanation 2 P(4 or 5):

    Multiples of 4 in 1 to 40 are:

    There are 10 multiples till 40 (since 4 \times 10 = 40) . So there are 10 multiples of 4 from 1 to 40.

    Multiple of 5 in 1 to 40 are:

    There are 8 multiples in 40 (since 5 \times 8 = 40). So there are 8 multiples of 5 from 1 to 40.

    Common Multiples of 4 and 5 in 1 to 40 is,

    20 and 40 only 2

    So, the probability of 4 or 5 is,

    P(\text {mult of 4})+P(\text {mult of 5}) -P(\text {mult of 4 and 5})

    =\frac{10}{40} +\frac{8}{40} -\frac{2}{40}

    =\frac{18}{40} -\frac{2}{40}

    =\frac{16}{40}

    =\frac{2}{5}

    So the probability of 4 or 5 is \frac{2}{5}.