two numbers r chosen from 1,3,5 149,151 and multiplied in all possible ways the number - Maths - Permutations and Combinations

Question

two numbers r chosen from 1,3,5 149,151 and multiplied in all
possible ways the number of ways which will give us the product a
multiple of 5 is : a 75 b 1020 c 95 d 1030

Rahul Raj · Accepted Answer

Dear student

if total number of terms in series = nthen 151=2+(n-1)*2n=76so total terms = 76multiples of 5 are 5,15,25,
145145=2+(m-1)*10m=15remaining terms = n-m=61we get multiple of 5 if we multiply any of the m numbers with the remaining numbers=15*61=915we ger also multiple of 5, if we multiply two numbers among the 'm' numbersno of ways =C215=14*152=105total ways=915+105=1020

regards

two numbers r chosen from 1,3,5.....149,151 and multiplied in all possible ways. the number of ways which will give us the product a multiple of 5 is : a 75 b 1020 c 95 d 1030