Answer: 4
<em><u>NOTE: ONLY REFER FIRST METHOD IF YOU ARE FROM CLASSES BELOW 5TH GRADE AND IF YOU KNOW THEM BOTH ITS OK.</u></em>
First we list factors of both 28 & 78
28: 1,2,4,7,14,28
78: 1,2,3,4,6,8,9,12,18,24,36,72
Now the common factors are, 1,2,4
And we know that 1<2<4
And thus 4 is the highest common factor
Another way is prime factorisation:
In this method, we need to find the prime factors of both the given numbers and find out the common factors and mutiply them.
So, 28: 2*2*7 and 72: 2*2*2*3*3
In now we see that, 2*2 is common in both common prime factors of both 28&72, Thus we get 2*2, And after solving it we get the highest common factor as 4
