It is given that, ∑x2=2830‌ and ‌∑x=170 The increase in ∑x=10 and increase in, ∑x2‌‌=(30)2−(20)2 ‌‌=900−400 ‌‌=500 So ∑x‌‌=170+10 ‌‌=180 And, ∑x2‌‌=2830+500 ‌‌=3330 So, the variance is calculated by ‌