① A number, minus the product of 3.5 and 4, the difference is 1 / 2 of 20, how much is this number ② What is the difference between the reciprocal of 2 and the sum of 2.5 divided by the quotient of 1 / 2, minus the quotient of 0.5 divided by 1 / 4? ③ Simple operation 1 / 5 △ 12 + 4 / 5 × 1 / 13 ③ Simple operation 1 / 5 △ 13 + 4 / 5 × 1 / 13

① A number, minus the product of 3.5 and 4, the difference is 1 / 2 of 20, how much is this number ② What is the difference between the reciprocal of 2 and the sum of 2.5 divided by the quotient of 1 / 2, minus the quotient of 0.5 divided by 1 / 4? ③ Simple operation 1 / 5 △ 12 + 4 / 5 × 1 / 13 ③ Simple operation 1 / 5 △ 13 + 4 / 5 × 1 / 13

1、x-3.5*4=20*1/2
x-14=10
x=24
2、(1/2+2.5)÷1.2-0.5÷（1/4）
=3÷1.2-0.5×4
=2.5-2
=0.5
3. Original formula = 1 / 5 × 1 / 12 + (1-1 / 5) × 1 / 13
=1/5×1/12+1/13-1/5×1/13
=1/5×（1/12-1/13）+1/13
=1/5×1/12×1/13+1/13
=（1/60+1）×1/13
=61/60×1/13
=61/780

Which is bigger, eight fifths or two fifths?

8 out of 15 > 2 out of 5
Because 2 out of 5 = 6 out of 15

How much is three and a half minus four and a fifth plus eight and a seventh minus thirty and a third?

Three and a half minus four and a fifth plus eight and a seventh minus thirty and a third
=(3-4+8-30)+(1/2-1/5+2/7-1/3)
=-23+3/10+2/7-1/3
=-23+41/70-1/3
=-23+53/210
=-22-157/210
=-22 and 157 / 210