What is the next number in the sequence? 7 18 29 40 51 ?

First find the difference between the numbers. Do this by subtracting the first number from the second number...

18

-7

11

Double check this to see if this runs true for the whole sequence by adding 11 to 18 to see if you have the correct answer.

11

18

29

Finally add the difference to the last known number in the sequence...

51

11

62

62 is the next number in the sequence.