If the average of 10x and 8y is greater than 70, and x is twice y, what is the least integer value of x ? Choices
A) 12 B) 14 C) 16 D) 10 E) 20
Substitution can be used in the following way:   Always start with the equation: x = 2y. It is more straight forward to manage as compared to the inequality.   Substitute y = x/2, not the other way because you need to find the minimum value of x. So you can get rid of y.   Now go on to the inequality. So 8y = 8x/2 = 4x   Now average of 10x and 4x is greater than 70. Average of 10x and 4x is 7x. So,   7x &gt; 70   x &gt; 10   Answer : 108 /2= 
<gadget id="calculator">8 /2</gadget>
<output>4</output>
4x   Now average of 10x and 4x is greater than 70. Average of 10x and 4x is 7x. So,   7x &gt; 70   x &gt; 10   Answer : 10
<result>D</result>
If the average of 10x and 8y is greater than 70, and x is twice y, what is the least integer value of x ?