Herdini, R., H. Suyitno, and P. Marwoto. “Mathematical Communication Skills Reviewed from Self-Efficacy by Using Problem Based Learning (PBL) Model Assisted With Manipulative Teaching Aids”. Journal of Primary Education, Vol. 8, no. 1, Aug. 2018, pp. 85-73, doi:10.15294/jpe.v8i1.25311.