(a+b)(c+d)(a+c)(b+d)= 1

200×(70×65? 30×35)2

100× 100× 105×95

≈ 24.5 > 10.828, so it can be concluded that whether you need help in math learning is 99.9% related to gender.

For 2×2 contingency table, the formula K2 = n (ad-BC) 2/[(a+b) (c+d) (a+c) (b+d)] cannot be simplified.

Extended data;

Independence test is a test method of statistics. Like fitness test, it belongs to X2 test (chi-square test), which is a hypothesis test to judge whether two factors are related or independent according to frequency data.

If we want to infer that the statement is H1:"X is related to Y", we can use independence test to examine whether the two variables are related, which can give the reliability of this judgment more accurately. Specifically, the value of the random variable K 2 (that is, the square of K) is calculated from the data in the table.

K2？ = n (AD-BC)? 2? /[(a+b)(c+d)(a+c)(b+d)], where n=a+b+c+d is the sample size.

The greater the value of K2, the greater the possibility that "X and Y are related".

Baidu encyclopedia-independence test