When calculating a question, Xiao careless mistakenly regards a number multiplied by 5 plus 30 as a number divided by 5 minus 30, and the result is 80, What's the number? What's the correct number?

When calculating a question, Xiao careless mistakenly regards a number multiplied by 5 plus 30 as a number divided by 5 minus 30, and the result is 80, What's the number? What's the correct number?

First, use his wrong algorithm to restore a certain number. Subtract 30 to get 80, which means that the quotient of 5 is:
80 + 30 = 110 divided by 5 is 110, indicating that the original number is 5 times of it: 110x5 = 550
The normal answer is 550x5 = 2750 2750-30 = 2720

Calculate 1 / 4 + 1 / 28 + 1 / 70 + 1 / 130 + 1 / 13

1 / 4 + 1 / 28 + 1 / 70 + 1 / 130 + 1 / 13 = 7 / 28 + 1 / 28 + 1 / 70 + 1 / 130 + 1 / 13 = 2 / 7 + 1 / 70 + 1 / 130 + 1 / 13 = 20 / 70 + 1 / 70 + 1 / 130 + 1 / 13 = 3 / 10 + 1 / 130 + 1 / 13 = 39 / 130 + 1 / 130 + 1 / 13 = 4 / 13 + 1 / 13 = 5 / 13

How to calculate 1 / 4 plus 1 / 28 plus 1 / 70 plus 1 / 130 plus 1 / 208?
How to calculate 1 / 4 + 1 / 28 + 1 / 70 + 1 / 130 + 1 / 208?

1/4+1/28+1/70+1/130+1/208=1/(1*4)+1/(4*7)+1/(7*10)+1/(10*13)+1/(13*16)=1/3*[(1/1-1/4)+(1/4-1/7)+(1/7-1/10)+(1/10-1/13)+(1/13-1/16)]=1/3*(1-1/16)=(1/3)*(15/16)=5/16

How to solve the equation of (60 + 84) x divided by 2 = 3384?

（60+84）x÷2＝3384
144X÷2＝3384
72X＝3384
X＝3384÷72
X＝47