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.