A group of pupils calculated their average score for a Mathematics test. If one of them scored 9 marks more, their average score would
be 81. If one of them scored 3 marks less, their average score would
be 78. How many pupils were there in the group?

4

Step-by-step explanation: +9-(-3)=12

81-78=3

so 12/3=4

3< x< 5

step-by-step explanation:

|x - 4| < 1

there are two solutions, one positive and one negative.   remember to flip the inequality when taking the negative solution

x-4 < 1       x-4 > -1

add 4 to each side

x-4+4 < 1+4       x-4+4 > -1+4

x< 5                 x> 3

3< x< 5