The idea is to add all three numbers, then divide the result by 3 (because there are 3 numbers).
The Arithmetic mean of 34 and 102 is 68.To find the Arithmetic mean (average) of any amount of numbers, add all the numbers together, then divide by the number of numbers.So:(34+102)/2=68
LCM(68, 102) = 204 HCF(68, 102) = 34
68/102 = 34/51
-68
102
170
34
102 is almost average. Given the fluctuations among tests and various sources of error, it is likely that your 7 year old is average.
34, 68, 102, 136, 170, 204, 238, 272, 306, 340, . . .
1,2,17,34
1, 2, 4, 17, 34, 68 1, 2, 3, 6, 17, 34, 51, 102
34 + 4x=102 4x=68 x=17