Ed has 4 cards. There is a number on each card. Three of the numbers are 12, 6 and 15. The mean of the numbers is 10. What is the fourth number?
To find the mean you add all the numbers together and divide by the number of numbers. Call the fourth number x. Then we know that (12+6+15+x)/4 =10. then multiply both sides by 4 to get 12+6+15+x=40 which is 33+x=40. And subtracting 33 from 40 gives x=7. The fourth number is 7.
SP
Related Maths GCSE answers
All answers ▸How do I expand (x+a)(x+b)? (plus example)
How can i use completing the square to factorise and solve equations
A ladder 6·8m long is leaning against a wall. The foot of the ladder is 1·5m from the wall. Calculate the distance the ladder reaches up the wall.
There are 9 counters in a bag. 7 of the counters are green. 2 of the counters are blue. Ria takes at random two counters from the bag. Work out the probability that Ria takes one counter of each colour. You must show your working.