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# If we toss a pair of dice, what is the probability that a sum of 7 will appear?

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If we toss a pair of dice, what is the probability that a sum of 7 will appear?

A./ 7/36

B. 1/6

C. 1/2

D. 1/36

Four coins are tossed at the same time. What is the probability that exactly 3 heads will appear?

A. 1/2

B. 1/4

C. 1/16

D. 1/8

May 8, 2020

#1
+1

36 possible rolls

6 1

5 2

4 3    are all 7's   and two ways of rolling each of the,      6/36 = 1/6

May 8, 2020
#2
+4

So basically we first need to figure out how much pairs that add to 7.

1,6

6,1

2,5

5,2

3,4

4,3

There are 6*6 = 36 possible outcomes,  so 6/36 = 1/6

See guest's post below for 2).

If you don't understand anything feel free to ask.

May 8, 2020
edited by hugomimihu  May 8, 2020
#3
+1

Hmmmm       16 possibilities for the coin toss

there are 4 possibles for EXACTLY 3 heads

HHHT

HHTH

HTHH

THHH       4 OUT OF 16 =   1/4

May 8, 2020
#4
+3

Intresting point.

There are 4 ways of only 1 heads,

HTTT

THTT

TTHT
TTTH

HHTT

HTHT
HTTH

THHT

THTH

TTHH

HHHT
HHTH
HTHH
THHH

HHHH

TTTT

Good point it's 4/16

I'll revise my answer thanks for the correction!

hugomimihu  May 8, 2020
edited by hugomimihu  May 8, 2020
#5
0

The probability is =4! / [3!.1!.2^4] =24 /[6 x 16] = 1/4

Guest May 8, 2020