BECE Mathematics 2018 Paper

Since selection is from 1 to 20 , number of sample space being selected from = $20$Probability is calculated by the formula below:We have to list all the numbers divisible by 3 (multiples of 3 ) from 1 to 20 to know how many numbers divisible by 3 in the sampleNumbers divisible by 3 from 1 to $20=3,6,9,12,15$ and 18Hence 6 of the numbers are divisible by 3Substite the number of numbers divisible by 3 and the total sample space into the probability formulaCancel out2 goes into 6, $3$ times and 20, 10 times