题目内容：

请教几道数学题（列式计算）
①2/3与1/2的和去除2/3与1/6的差,商是多少?
②一个数的1/2比它的4/5少30,这个数是多少?
③甲数的25%等于乙数的2/3,乙数是72,甲数是多少?
④一个数是36,另一个数是它的5/12,则这两个数的和是多少?
⑤一个数的4倍减去这个数的本身,差是42.6,求这个数.
⑥某数的4/9比6/5的5/4倍多21/10,这个数是多少?
⑦一个数的1/2加上1/2的倒数,和是3,这个数是多少?
⑧15的2/3比一个数的4倍少12,这个数是多少?
⑨1/5与1/6的和除以它们的差,商是多少?

优质解答

1. (2/3 +1/2)/(2/3 -1/6) = (4/6+3/6)/(4/6 -1/6) = (7/6)/(3/6) = 7/3
2. 30/(4/5 - 1/2) = 30/(8/10 - 5/10) = 30/(3/10) = 100
3. (72*2/3)/25% = 48/25% = 192
4. 36 + 36*5/12 = 36 + 15 = 51
5. 42.6/3 = 14.2
6. 4a/9 - (6/5)*(5/4) = 21/10, 4a/9 = 21/10 + 3/2 = 21/10 + 15/10 = 36/10 = 18/5
a = (18/5)*(9/4) = 81/10
7. a/2 + 1/(1/2) = a/2 + 2 = 3, a/2 = 1, a = 2
8. 4a - 15*2/3 = 12, 4a - 10 = 12, 4a = 22, a = 11/2
9. (1/5 + 1/6)/(1/5 -1/6) = (6/30 + 5/30)/(6/30 - 5/30) = (11/30)/(1/30) = 11