X + 9 = 16
explanation : he bought nine more coins which made it 16. to find out how many coins he sold you would solve the equation then divide by 2.
Brushing your teeth everyday
Answer:

Step-by-step explanation:
3 envelopes having 2 red card
2 envelopes having 1 red card and 1 black card
1 envelope having 2 black cards
We are given that . An envelope is selected at random and a card is withdrawn and found to be red.
So, No. of ways of envelope having red card = 3+2 = 5
No. of required ways of envelope having 1 red card and 1 black card = 2
So, probability of getting an envelope having 1 red card and 1 black card = 
Hence The chance the other card is black is 
<span>3
--- </span>-2 = 8<span>
y
</span>3
--- = 8+2
y
3
--- = 10
y
3
3
y = ------
10