Question

a coin whose faces are marked 3 and 5 is tossed 4 times . then the probability that the sum of the numbers thrown is greater than 15 is
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Answer 1

The probability that  the sum of the numbers thrown is greater than 15 is

​11/16.

Total no. of cases = 2^4=16

the cases in which Sum of numbers is less than 15 are 5 cases

1st case : 3333

2nd case : 3335

3rd case : 3353

4th  case : 3533

5th   case : 5333

therefore the no. of cases in which the sum of numbers are greater than 15

= Total cases - no. of case in which sum is less than 15

=16 -5 = 11 cases.

Those 11 cases are: 5555,5533,3553,3355,5335,5353,3535,5553,5355,5535,3555

therefore the probability that the sum of the numbers thrown is greater than 15 =  the no. of cases in which the sum of numbers are greater than 15/TOTAL NO. OF CASES

= 11/16