Equal Means

What value of x makes the mean of the first three numbers in this list equal to the mean of the other four?
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative


What value of $x$ makes the mean of the first three numbers in this list equal to the mean of the last four?$$15\qquad 5 \qquad x \qquad 7 \qquad 9 \qquad 17 \qquad$$