Rista, B.V., Agung, A.G. and Ujianti, P.R. 2021. Validity and Reliability: An Ability Assessment Instrument to Identify the Number Concept. Indonesian Journal of Educational Research and Review. 3, 3 (Jan. 2021), 144–152. DOI:https://doi.org/10.23887/ijerr.v3i3.30614.