Question

Paco uses a spinner to select a number from 1 through 5, each with equal probability. Manu uses a different spinner to select a number from 1 through 10, each with equal probability. What is the probability that the product of Manu's number and Paco's number is less than 30?

Answer 1

P1=1*1/2=1/2
P2=4/5*1/5=4/25
P3=3/5*1/5=3/25
P4=2/5*1/10=2/50
P=1/2+4/25+3/25+2/50=41/50
The probability that the product of Manu's number and Paco's number is less than 30 is 41/50.

Answer 2

The possible outcomes are; every number from 1 to 5, times every number from 1 to 10. Than makes 5 x 10 different outomes.

Then you need to take in account how many of them are smaller thatn 30. The easiest way is to count how many are greater or equal than 30. If you do that you will find 9 results greater or equal than 30: 10x5, 1x4, 10x3, 9x5, 9x4, 8x5, 8x4, 7x5, 6x5.

Then, there are 41 products that are less than 30 and the probability is 41/50= 0.82