How to calculate the mathematical formula?

How to calculate the mathematical formula?

According to the title listed formula for calculation, the order of calculation is: brackets, first calculate the brackets, then calculate multiplication and division, and then calculate addition and subtraction

1. What is the sum of 2 / 5 and 1 / 3 of a number?
2. 3 / 5 of a number plus 3 / 4 of this number is less than 15. What is this number?
3. What is the quotient of the sum of 3 / 4 and its reciprocal divided by the product of 7 / 9 and 4 / 5?
4. 80% of a number is 12 more than 2 / 3 of the number. What is the number? (equation)
5. What's the difference between increasing it by 20% and subtracting 2.5?
You don't have to calculate. If you have one tonight,

① To see this kind of problem, we should first set the unknowns as X
(2/5)X+1/3=1
② The title seems to be wrong
③（3/4+4/3）/(7/9*4/5)
④ Let the unknown be X
80%X-2/3X=12
⑤ Let the unknown be X
25*（1+20%）-2.5
After that, it's better to check it
Answer: ① 5 / 3
③175/48
④90
⑤27.5

. formula calculation
What is the product of 1.4 minus one fourth of the difference multiplied by three fifths?
2. What is the sum of two-thirds and three-quarters of a number?
3. One third and one half is 50% more than 1.5 times of X?
What is the sum of the product of 4.3.4 and 20% plus the product of one and a fifth and 20%?

1.(4-1/4)*3/5=9/20
2.(1-3/4)/(2/3)=3/8
3.()=[(1.5x)*(1+50%)] x=14/9
4.3.4*20%+(6/5)*20%=0.92
Note: one third and one half cannot be typed, so I use 7 / 2
One and a fifth can't be typed, so I use 6 / 5