英文maths題....

1.

Let x be the no. of $2 coins,
y be the no. of $5 coins,

x + y = 60...{1}
2x+5y=195..{2}

From {1} , x=60-y,

Sub. {3} into {2} ,
2(60-y) + 5y = 195
120 - 2y + 5y = 195
120 + 3y =195
3y = 75
y =25

Sub. y = 25 into {1}
x + y = 60
x + 25 = 60
x = 35''

There are 35 $2 coins,
25 $5 coins .

2.

Let x be the age of the boy ,
y be the age of his father ,

x = 1/3y + 1....................{1}
x + 5 =1/2( y + 5 ) - 4.......{2}

Sub. {1} into [2},
(1/3y + 1 ) + 5 = 1/2( y + 5 ) - 4
1/3y + 1 + 5 = 1/2y + 5/2 - 4
7.5 = 1/6y
y=45

so his father is 45 years old .

10
x = no of $2 coin; y = no of $5 coin
x+y = 60
2x+5y=195
2 (60-y) + 5y = 195
120-2y+5y=195
3y=75
y=25
x+y=60
x=60-25
x=35

2)
x=age of a boy; y=age of father
x = 1/3y+1
x+5=1/2(y+5)-4
x+5=0.5y+2.5-4
1/3y+1=0.5y-6.5
7.5=-1/3y+1/2y
45=-2y+3y
45=y
x=1/3(45)+1
x=16

y is $5, x is $2
2x + 5y = 195 ---------------------1
x+y = 60 ----------------------------2

x is the boy, y is father
x = (y / 3) + 1 ----------------------1
x+5 = y+5-4 ------------------------2

計就自己計啦

Q1.
Ans: $2 = 35pcs $5 = 25pcs

Q2

Ans: present age of father = 44year old