Christopher and his brother christian was playing toys christopher had 17x51 toys christian had 14x84 who had more toys christopher or christian

Rather than multiplying the actual numbers shown, try estimating and then comparing the two products by first rounding off.  Thus, 17 times 51 could be approx. by 17 times 50, or about 850.  14 times 84 could be approx. by 15 times 84, or 840+420, or 1260.  Obviously the 2nd product is greater. 

Again:  Use estimation in this type of problem.  15 times 84 is the same as
(10 times 84) plus (5 times 84), or 840 plus 420.  800 plus 400 is 1200; 40 plus 20 is 60; thus, we get 1260, which is obviously a lot more than 17 times 51.