英數方程應用題

Let the age of Sam now be y.

(y-5)/2=30-5

(y-5)/2=25

y-5=50

y=55

Sam is 55 years old now.

Joe is now 30, so five years ago he was 25, and Sam was 2 times 25, ie 50 (five years ago).
As a result, Sam is 50+5=55 now!

No any equation you need to handle. Just calculate it by your heart!

To learn mathematics better, use equation is ok, but some time if you can calculate the question without setting equation, you can learn more.

1)Let the previous age of Sam be x.
x/2=30-5
x/2=25
x =50
∴The age of Sam now is 50+5=55.
or
2.Let the age of Sam now be x.
x-5=2×(30-5)
x-5=50
x=55
∴The age of Sam now is 55.

Let x be the age of Sam now,
x-5=(30-5)*2
x-5=50
x=55
Therefore,the age of Sam is 55 now.

希望幫到你啦!=]

The age of Joe five years ago
= 30 - 5
= 25

The age of Sam five years ago
= 25 X 2
= 50

The age of Sam now
= 50 + 5
= 55

Let y be Sam's age five years ago
y/2+5=30
y/2=30-5
y=25x2
y=50
∴Sam is 50 years old now

2007-07-21 21:48:58 補充：
'.'Sam is 50 years old five years ago∴Sam is (50+5) i.e. 55 years old now

2007-07-21 21:50:16 補充：
完整的:Let y be Sam's age five years agoy/2 5=30y/2=30-5y=25x2y=50'.'Sam is 50 years old five years ago∴Sam is (50 5) i.e. 55 years old now