MathRevolution wrote:
Forget conventional ways of solving math questions. In PS, IVY approach is the easiest and quickest way to find the answer.
The integer x has a tens digit of 6 and a units digit of 7. The units digit of integer y is 8. The product of x and y has a tens digit of 8. Which of the following is a possible tens digit of integer y?
A. 3
B. 4
C. 5
D. 6
E. 7
Let x be 67 and y be a8. Then the product of x and y can be written as (60+7)*(10a+8)=600a + 480+70a+56=600a+536+70a. Since 600a dose not affect on the tens digit we can ignore 600a.
So tens digit should be the unit of 3+7a. That means 3+7a =8, 18, 28, 38, 48 or 58 (since 3+7a<=3+7*9=66) --->7a=5, 15, 25, 35, 45, 55. So the only possibility is a=5.
So the answer is (C).
Hello,
Can you please elaborate how you arrived to below conclusion :-
"So tens digit should be the unit of 3+7a. That means 3+7a =8, 18, 28, 38, 48 or 58 (since 3+7a<=3+7*9=66) --->7a=5, 15, 25, 35, 45, 55. So the only possibility is a=5"
Thanks.