Solution: Idea: Proportional distribution
If you unsubscribe from 2 copies of each magazine, you will unsubscribe from 4 copies, that is, you have also subscribed to 90 copies of Mathematics Newspaper and Students' World.
So the original subscription of Journal of Mathematics was (94-4)×8/(8+7)+2=50 copies.
Original student world: 94-50=44 books.
There are two interest groups, common sense and computer. The number of people in the two groups is 5: 3 (it should be 3: 5, otherwise the number of people calculated is a score? ), from the common sense group of 4 people to the computer group, then the ratio of the common sense group to the computer group is 1: 2, which is the number of the original two groups.
Solution: thinking: change with constancy, that is, find the invariable quantity in each question first.
In this question, the constant is the sum of two groups of people and is regarded as the unit "1"
Because the ratio of the two groups is 3: 5, the common sense group accounts for 3/(5+3) of the sum of the two groups.
Because there are four people from the common sense group to the computer group, and the ratio of the common sense group to the computer group is 1: 2, then the common sense group accounts for 1/( 1+2) of the sum of the two groups.
So four people account for [3/(5+3)-1/(1+2)] of the sum of the two groups.
Therefore, the total number of people in the two groups is 4 ÷ [3/(5+3)-1(1+2)] = 96.
Therefore, the common sense group was originally 96×3/(5+3)=36 people.
The computer group originally had: 96-36=60 people.
Team A, Team B and Team C jointly built a road. The ratio of meters built by Party A and Party C is 2: 5. Team A built 1/5 less than team B, and team C built 250 kilometers. How much did Team A and Team B build?
Solution: Because the ratio between team A and team C is 2: 5, team C repaired 250 kilometers.
Therefore, Team A repaired: 250×2/5= 100 km.
Because Team A has fewer repairs than Team B 1/5.
Therefore, Team B revised:100 ÷ (1-1/5) =125 km.