# Probability (1 Viewer)

#### taker0

##### Member
Ok i suck at probability and i relay need to work some thigs out beofr tomrow. first, how do i use the npr/ncr button on the calc to work out combs/perms...im confused at when to use that method and how to do it.

also can some1 check these answers for me:

(a) On a bridge, the toll of 2.50 is paid in coins collected by a machiene. the macheien only accpets \$2, \$1 and 50c coins.

(i) list the combinations used to pay the 2.50

(ii) jill has 3 two dollar coins, 6 one dollar coins and 2 50c coins. she selects 2 at random. wat is the robability the she selects exactly 2.50?

(iii) at the end of the day the macheine contains x two-dollar coins, y one dollar coins and w 50c coins. write an expression for the total value of coins

I:
1,1,50c
50,50,50
2,50

II: 2/10x2/9 = 2/45

III: v=x+y+w

#### savio23q

##### Band
(i) You'd need 5 50cent coins, not 3. Rest is okay.

(ii) She can only pick out 2 coins. So she needs \$2 and then 50cents.

Probability of selecting \$2 1st = 3/11
Probability of selecting 50 cents 2nd = 2/10

Probability of selecting 50 1st = 2/11
Probability of selecting \$2 2nd = 3/10

SO 3/11 x 2/10 + 2/11 x 3/10 = 6/55

NOT 100% SURE! Dont rely on me LOL.

(iii) T = 2x + y + 0.50w