5x-(20-x)× 1=70

5x-20+x=70

6x=90

x= 15

Answer: If the score is 70, you should answer 15 correctly.

86. Solution: After x hours, the distance between them is19.8km..

(4.2+4.8)x= 19.8-6.3

9x= 13.5

x= 1.5

A: After 1.5 hours, the distance between them is 19.8 kilometers.

87. Solution: Only when X people are transferred from Team B can Team A be half the number of Team B..

(40+2+x)=( 186-x)÷2

84+2x= 186-x

3x= 102

x=34

A: To make the number of team A half that of team B, we need 34 people from team B..

88. Solution: There are X people in each copy.

(5+4+3+5)x=34

x=2

At least 2×3=6 (person) and at most 2×5= 10 (person).

89. Solution: (1) Suppose that after X years, the mother's age is exactly three times that of her daughter.

38+x=( 12+x)×3

38+x=36+3x

2x=2

x= 1

That is 1 year later, the mother's age is exactly three times that of her daughter.

(2) The original price of this schoolbag is X yuan.

X×0.7×0.5=7

0.35X=7

X=20

That is, the original price of this schoolbag is 20 yuan.

90. Solution: Let the first number be X, then the second number is x+ 1, the third number is x+7, and the fourth number is x+8.

x+(x+ 1)+(x+7)+(x+8)= 100

4x+ 16= 100

4x=84

x=2 1

These days are 2 1, 22, 28 and 29 respectively.

9 1, the condition is incomplete.

92. Solution: Suppose he saved X yuan at first.

x+x×2.7%×3=5405

( 1+0.08 1)x=5404

x=5000

At first, he saved 5000 yuan.

93. The profit rate of Party A is x%, and that of Party B is y%.

1500 x % = 1800( 1+0.2)×0.8- 1500

x= 15.2

1500y % = 1800×0.9- 1500

y=8

So A's profit margin is high.

Solution: Suppose he bought X jellies.

( 15/2)x+(40-x) 10/3 = 175

45x+800-20x= 1050

25x=250

x= 10

He bought 10 jelly.