Question 408094
1. Because it's possible to put zero objects into three groups, but it is impossible to put three objects into zero groups (assuming all three objects are distributed).

2. If {{{(2x+1)/(x+1) = 2}}}, then by cross-multiplying, {{{2x+1 = 2(x+1) = 2x+2}}}, {{{1 = 2}}}, contradiction.

3. {{{1/a + 1/b = (b+a)/ab = 7/10}}}.