[Mathematics] There are 27 RMB in 5 yuan, 2 yuan. How much is the RMB in 99 yuan, 2 yuan and 5 yuan?
Assuming that there are X RMB in 2 yuan and Y RMB in 5 yuan, the equations can be listed according to the meaning of the question.
2X+5Y=99 ①
X+Y=27 ②
Add 1-②*2 to get it.
3Y=45
Y= 15
Substitute Y= 15 into ② to get X+ 15=27.
The solution is X= 12.
Then 2 yuan's 12 RMB and 5 yuan's 15 RMB.