If you want to apply conditional validation on 'English' or 'Statstics', then you need to add 'Maths' input as '50'
{{resultinfoForm.controls?.maths?.errors?.minNumber.message}}
Conditional validation will be applied if the 'Maths' field have value of '50'
you can enter min number upto 35
Conditional Expression with type 'string'
{{resultinfoForm.controls?.statstics?.errors?.minNumber.message}}